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* Update all default taskq settingsBrian Behlendorf2015-06-251-1/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Over the years the default values for the taskqs used on Linux have differed slightly from illumos. In the vast majority of cases this was done to avoid creating an obnoxious number of idle threads which would pollute the process listing. With the addition of support for dynamic taskqs all multi-threaded queues should be created as dynamic taskqs. This allows us to get the best of both worlds. * The illumos default values for the I/O pipeline can be restored. These values are known to work well for most workloads. The only exception is the zio write interrupt taskq which is changed to ZTI_P(12, 8). At least under Linux more threads has been shown to improve performance, see commit 7e55f4e. * Reduces the number of idle threads on the system when it's not under heavy load. The maximum number of threads will only be created when they are required. * Remove the vdev_file_taskq and rely on the system_taskq instead which is now dynamic and may have up to 64-threads. Again this brings us back inline with upstream. * Tasks dispatched with taskq_dispatch_ent() are allowed to use dynamic taskqs. The Linux taskq implementation supports this. Signed-off-by: Brian Behlendorf <[email protected]> Signed-off-by: Tim Chase <[email protected]> Closes #3507
* Add taskq_wait_outstanding() functionBrian Behlendorf2015-06-111-0/+6
| | | | | | | | | SPL commit behlendorf/spl@9cef1b5 adds the taskq_wait_outstanding() interface. See the commit log for the full justification for this addition. This patch adds the required user space counterpart. Signed-off-by: Brian Behlendorf <[email protected]> Signed-off-by: Tim Chase <[email protected]>
* Illumos 5497 - lock contention on arcs_mtxPrakash Surya2015-06-111-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Reviewed by: George Wilson <[email protected]> Reviewed by: Matthew Ahrens <[email protected]> Reviewed by: Richard Elling <[email protected]> Approved by: Dan McDonald <[email protected]> Porting notes and other significant code changes: The illumos 5368 patch (ARC should cache more metadata), which was never picked up by ZoL, is mostly reverted by this patch. Since ZoL relies on the kernel asynchronously calling the shrinker to actually reap memory, the shrinker wakes up arc_reclaim_waiters_cv every time it runs. The arc_adapt_thread() function no longer calls arc_do_user_evicts() since the newly-added arc_user_evicts_thread() calls it periodically. Notable conflicting ZoL commits which conflicted with this patch or whose effects are either duplicated or un-done by this patch: 302f753 - Integrate ARC more tightly with Linux 39e055c - Adjust arc_p based on "bytes" in arc_shrink f521ce1 - Allow "arc_p" to drop to zero or grow to "arc_c" 77765b5 - Remove "arc_meta_used" from arc_adjust calculation 94520ca - Prune metadata from ghost lists in arc_adjust_meta Trace support for multilist_insert() and multilist_remove() has been added and produces the following output: fio-12498 [077] .... 112936.448324: zfs_multilist__insert: ml { offset 240 numsublists 80 sublistidx 63 } fio-12498 [077] .... 112936.448347: zfs_multilist__remove: ml { offset 240 numsublists 80 sublistidx 29 } The following arcstats have been removed: recycle_miss - Used by arcstat.py and arc_summary.py, both of which have been updated appropriately. l2_writes_hdr_miss The following arcstats have been added: evict_not_enough - Number of times arc_evict_state() was unable to evict enough buffers to reach its target amount. evict_l2_skip - Number of times arc_evict_hdr() skipped eviction because it was being written to the l2arc. l2_writes_lock_retry - Replaces l2_writes_hdr_miss. Number of times l2arc_write_done() failed to acquire hash_lock (and re-tries). arc_meta_min - Shows the value of the zfs_arc_meta_min module parameter (see below). The "index" column of the "dbuf" kstat has been removed since it doesn't have a direct analog in the new multilist scheme. Additional multilist- related stats could be added in the future but would likely require extensions to the mulilist API. The following module parameters have been added: zfs_arc_evict_batch_limit - Number of ARC headers to free per sub-list before moving on to the next sub-list. zfs_arc_meta_min - Enforce a floor on the amount of metadata in the ARC. zfs_arc_num_sublists_per_state - Number of multilist sub-lists per ARC state. zfs_arc_overflow_shift - Controls amount by which the ARC must exceed the target size to be considered "overflowing". Ported-by: Tim Chase <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]
* Illumos #5244 - zio pipeline callers should explicitly invoke next stageGeorge Wilson2015-04-301-0/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | 5244 zio pipeline callers should explicitly invoke next stage Reviewed by: Adam Leventhal <[email protected]> Reviewed by: Alex Reece <[email protected]> Reviewed by: Christopher Siden <[email protected]> Reviewed by: Matthew Ahrens <[email protected]> Reviewed by: Richard Elling <[email protected]> Reviewed by: Dan McDonald <[email protected]> Reviewed by: Steven Hartland <[email protected]> Approved by: Gordon Ross <[email protected]> References: https://www.illumos.org/issues/5244 https://github.com/illumos/illumos-gate/commit/738f37b Porting Notes: 1. The unported "2932 support crash dumps to raidz, etc. pools" caused a merge conflict due to a copyright difference in module/zfs/vdev_raidz.c. 2. The unported "4128 disks in zpools never go away when pulled" and additional Linux-specific changes caused merge conflicts in module/zfs/vdev_disk.c. Ported-by: Richard Yao <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #2828
* Illumos 5134 - if ZFS_DEBUG or debug= is set, libzpool should enable debug ↵Matthew Ahrens2015-04-281-0/+3
| | | | | | | | | | | | | | | | | | | | | | prints 5134 if ZFS_DEBUG or debug= is set, libzpool should enable debug prints Reviewed by: Adam Leventhal <[email protected]> Reviewed by: Christopher Siden <[email protected]> Reviewed by: George Wilson <[email protected]> Reviewed by: Saso Kiselkov <[email protected]> Approved by: Dan McDonald <[email protected]> References: https://www.illumos.org/projects/illumos-gate/issues/5134 https://github.com/illumos/illumos-gate/commit/7fa49ea Porting notes: Added dprintf_setup() to main in zfs_main.c and zpool_main.c. Ported by: Turbo Fredriksson <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #2669
* Change VERIFY to ASSERT in mutex_destroy()Brian Behlendorf2015-02-111-1/+1
| | | | | | | | | | | | | There have been multiple reports of 'zdb' tripping the VERIFY in mutex_destroy() because pthread_mutex_destroy() returns EBUSY. Exactly how this can happen still needs to be explained, but this doesn't strictly need to be fatal for non-debug builds. Therefore, this patch converts the VERIFY to an ASSERT until the root cause is determined and resolved. Signed-off-by: Brian Behlendorf <[email protected]> Issue #2027
* Read spl_hostid module parameter before gethostid()Chunwei Chen2015-02-041-1/+25
| | | | | | | | | | If spl_hostid is set via module parameter, it's likely different from gethostid(). Therefore, the userspace tool should read it first before falling back to gethostid(). Signed-off-by: Chunwei Chen <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #3034
* Mark IO pipeline with PF_FSTRANSBrian Behlendorf2015-01-161-0/+17
| | | | | | | | | | In order to avoid deadlocking in the IO pipeline it is critical that pageout be avoided during direct memory reclaim. This ensures that the pipeline threads can always make forward progress and never end up blocking on a DMU transaction. For this very reason Linux now provides the PF_FSTRANS flag which may be set in the process context. Signed-off-by: Brian Behlendorf <[email protected]>
* Swap DTRACE_PROBE* with Linux tracepointsPrakash Surya2014-11-171-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch leverages Linux tracepoints from within the ZFS on Linux code base. It also refactors the debug code to bring it back in sync with Illumos. The information exported via tracepoints can be used for a variety of reasons (e.g. debugging, tuning, general exploration/understanding, etc). It is advantageous to use Linux tracepoints as the mechanism to export this kind of information (as opposed to something else) for a number of reasons: * A number of external tools can make use of our tracepoints "automatically" (e.g. perf, systemtap) * Tracepoints are designed to be extremely cheap when disabled * It's one of the "accepted" ways to export this kind of information; many other kernel subsystems use tracepoints too. Unfortunately, though, there are a few caveats as well: * Linux tracepoints appear to only be available to GPL licensed modules due to the way certain kernel functions are exported. Thus, to actually make use of the tracepoints introduced by this patch, one might have to patch and re-compile the kernel; exporting the necessary functions to non-GPL modules. * Prior to upstream kernel version v3.14-rc6-30-g66cc69e, Linux tracepoints are not available for unsigned kernel modules (tracepoints will get disabled due to the module's 'F' taint). Thus, one either has to sign the zfs kernel module prior to loading it, or use a kernel versioned v3.14-rc6-30-g66cc69e or newer. Assuming the above two requirements are satisfied, lets look at an example of how this patch can be used and what information it exposes (all commands run as 'root'): # list all zfs tracepoints available $ ls /sys/kernel/debug/tracing/events/zfs enable filter zfs_arc__delete zfs_arc__evict zfs_arc__hit zfs_arc__miss zfs_l2arc__evict zfs_l2arc__hit zfs_l2arc__iodone zfs_l2arc__miss zfs_l2arc__read zfs_l2arc__write zfs_new_state__mfu zfs_new_state__mru # enable all zfs tracepoints, clear the tracepoint ring buffer $ echo 1 > /sys/kernel/debug/tracing/events/zfs/enable $ echo 0 > /sys/kernel/debug/tracing/trace # import zpool called 'tank', inspect tracepoint data (each line was # truncated, they're too long for a commit message otherwise) $ zpool import tank $ cat /sys/kernel/debug/tracing/trace | head -n35 # tracer: nop # # entries-in-buffer/entries-written: 1219/1219 #P:8 # # _-----=> irqs-off # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / delay # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | lt-zpool-30132 [003] .... 91344.200050: zfs_arc__miss: hdr... z_rd_int/0-30156 [003] .... 91344.200611: zfs_new_state__mru... lt-zpool-30132 [003] .... 91344.201173: zfs_arc__miss: hdr... z_rd_int/1-30157 [003] .... 91344.201756: zfs_new_state__mru... lt-zpool-30132 [003] .... 91344.201795: zfs_arc__miss: hdr... z_rd_int/2-30158 [003] .... 91344.202099: zfs_new_state__mru... lt-zpool-30132 [003] .... 91344.202126: zfs_arc__hit: hdr ... lt-zpool-30132 [003] .... 91344.202130: zfs_arc__hit: hdr ... lt-zpool-30132 [003] .... 91344.202134: zfs_arc__hit: hdr ... lt-zpool-30132 [003] .... 91344.202146: zfs_arc__miss: hdr... z_rd_int/3-30159 [003] .... 91344.202457: zfs_new_state__mru... lt-zpool-30132 [003] .... 91344.202484: zfs_arc__miss: hdr... z_rd_int/4-30160 [003] .... 91344.202866: zfs_new_state__mru... lt-zpool-30132 [003] .... 91344.202891: zfs_arc__hit: hdr ... lt-zpool-30132 [001] .... 91344.203034: zfs_arc__miss: hdr... z_rd_iss/1-30149 [001] .... 91344.203749: zfs_new_state__mru... lt-zpool-30132 [001] .... 91344.203789: zfs_arc__hit: hdr ... lt-zpool-30132 [001] .... 91344.203878: zfs_arc__miss: hdr... z_rd_iss/3-30151 [001] .... 91344.204315: zfs_new_state__mru... lt-zpool-30132 [001] .... 91344.204332: zfs_arc__hit: hdr ... lt-zpool-30132 [001] .... 91344.204337: zfs_arc__hit: hdr ... lt-zpool-30132 [001] .... 91344.204352: zfs_arc__hit: hdr ... lt-zpool-30132 [001] .... 91344.204356: zfs_arc__hit: hdr ... lt-zpool-30132 [001] .... 91344.204360: zfs_arc__hit: hdr ... To highlight the kind of detailed information that is being exported using this infrastructure, I've taken the first tracepoint line from the output above and reformatted it such that it fits in 80 columns: lt-zpool-30132 [003] .... 91344.200050: zfs_arc__miss: hdr { dva 0x1:0x40082 birth 15491 cksum0 0x163edbff3a flags 0x640 datacnt 1 type 1 size 2048 spa 3133524293419867460 state_type 0 access 0 mru_hits 0 mru_ghost_hits 0 mfu_hits 0 mfu_ghost_hits 0 l2_hits 0 refcount 1 } bp { dva0 0x1:0x40082 dva1 0x1:0x3000e5 dva2 0x1:0x5a006e cksum 0x163edbff3a:0x75af30b3dd6:0x1499263ff5f2b:0x288bd118815e00 lsize 2048 } zb { objset 0 object 0 level -1 blkid 0 } For the specific tracepoint shown here, 'zfs_arc__miss', data is exported detailing the arc_buf_hdr_t (hdr), blkptr_t (bp), and zbookmark_t (zb) that caused the ARC miss (down to the exact DVA!). This kind of precise and detailed information can be extremely valuable when trying to answer certain kinds of questions. For anybody unfamiliar but looking to build on this, I found the XFS source code along with the following three web links to be extremely helpful: * http://lwn.net/Articles/379903/ * http://lwn.net/Articles/381064/ * http://lwn.net/Articles/383362/ I should also node the more "boring" aspects of this patch: * The ZFS_LINUX_COMPILE_IFELSE autoconf macro was modified to support a sixth paramter. This parameter is used to populate the contents of the new conftest.h file. If no sixth parameter is provided, conftest.h will be empty. * The ZFS_LINUX_TRY_COMPILE_HEADER autoconf macro was introduced. This macro is nearly identical to the ZFS_LINUX_TRY_COMPILE macro, except it has support for a fifth option that is then passed as the sixth parameter to ZFS_LINUX_COMPILE_IFELSE. These autoconf changes were needed to test the availability of the Linux tracepoint macros. Due to the odd nature of the Linux tracepoint macro API, a separate ".h" must be created (the path and filename is used internally by the kernel's define_trace.h file). * The HAVE_DECLARE_EVENT_CLASS autoconf macro was introduced. This is to determine if we can safely enable the Linux tracepoint functionality. We need to selectively disable the tracepoint code due to the kernel exporting certain functions as GPL only. Without this check, the build process will fail at link time. In addition, the SET_ERROR macro was modified into a tracepoint as well. To do this, the 'sdt.h' file was moved into the 'include/sys' directory and now contains a userspace portion and a kernel space portion. The dprintf and zfs_dbgmsg* interfaces are now implemented as tracepoint as well. Signed-off-by: Prakash Surya <[email protected]> Signed-off-by: Ned Bass <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]>
* Update utsname supportBrian Behlendorf2014-10-171-4/+8
| | | | | | | | | | | | | | | | | | Modify the code to use the utsname() kernel function rather than a global variable. This results is cleaner more portable code because utsname() is already provided by the kernel and can be easily emulated in user space via uname(2). This means that it will behave consistently in both contexts. This is also has the benefit that it allows the removal of a few _KERNEL pre-processor conditions. And it also is a pre-requisite for a proper FUSE port because we need to provide a valid utsname. Finally, it allows us to remove this functionality from the SPL and all the related compatibility code. Signed-off-by: Brian Behlendorf <[email protected]> Issue #2757
* Make user stack limit configurableBrian Behlendorf2014-09-301-24/+24
| | | | | | | | | | | | | | | | | To aid in detecting and debugging stack overflow issues make the user space stack limit configurable via a new ZFS_STACK_SIZE environment variable. The value assigned to ZFS_STACK_SIZE will be used as the default stack size in bytes. Because this is mainly useful as a debugging aid in conjunction with ztest the stack limit is disabled by default. See the ztest(1) man page for additional details on using the ZFS_STACK_SIZE environment variable. Signed-off-by: Brian Behlendorf <[email protected]> Signed-off-by: Ned Bass <[email protected]> Closes #2743 Issue #2293
* lib/libzpool/kernel.c: Assert no owners in rw_destroy()Richard Yao2014-09-231-1/+1
| | | | | | | | | This is intended to cause ztest to fail when rw_destroy() is called on a rwlock that has owners. Signed-off-by: Richard Yao <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Issue #2330
* Remove obsolete comment about guard pagesNed Bass2014-09-221-6/+0
| | | | | | | | | | Remove an obsolete comment that refers to code removed by commit 79c6e4c4. The code and comment related to space consumed by guard pages in user-space stacks, which we no longer take into account. Signed-off-by: Ned Bass <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #2722
* Illumos 4757, 4913Matthew Ahrens2014-08-011-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | 4757 ZFS embedded-data block pointers ("zero block compression") 4913 zfs release should not be subject to space checks Reviewed by: Adam Leventhal <[email protected]> Reviewed by: Max Grossman <[email protected]> Reviewed by: George Wilson <[email protected]> Reviewed by: Christopher Siden <[email protected]> Reviewed by: Dan McDonald <[email protected]> Approved by: Dan McDonald <[email protected]> References: https://www.illumos.org/issues/4757 https://www.illumos.org/issues/4913 https://github.com/illumos/illumos-gate/commit/5d7b4d4 Porting notes: For compatibility with the fastpath code the zio_done() function needed to be updated. Because embedded-data block pointers do not require DVAs to be allocated the associated vdevs will not be marked and therefore should not be unmarked. Ported by: Tim Chase <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #2544
* Illumos #4374Matthew Ahrens2014-07-301-4/+2
| | | | | | | | | | | | | | | | | | | 4374 dn_free_ranges should use range_tree_t Reviewed by: George Wilson <[email protected]> Reviewed by: Max Grossman <[email protected]> Reviewed by: Christopher Siden <[email protected] Reviewed by: Garrett D'Amore <[email protected]> Reviewed by: Dan McDonald <[email protected]> Approved by: Dan McDonald <[email protected]> References: https://www.illumos.org/issues/4374 https://github.com/illumos/illumos-gate/commit/bf16b11 Ported by: Tim Chase <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #2531
* Illumos 4368, 4369.Matthew Ahrens2014-07-291-0/+1
| | | | | | | | | | | | | | | | | 4369 implement zfs bookmarks 4368 zfs send filesystems from readonly pools Reviewed by: Christopher Siden <[email protected]> Reviewed by: George Wilson <[email protected]> Approved by: Garrett D'Amore <[email protected]> References: https://www.illumos.org/issues/4369 https://www.illumos.org/issues/4368 https://github.com/illumos/illumos-gate/commit/78f1710 Ported by: Tim Chase <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #2530
* Illumos #4101, #4102, #4103, #4105, #4106George Wilson2014-07-221-0/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 4101 metaslab_debug should allow for fine-grained control 4102 space_maps should store more information about themselves 4103 space map object blocksize should be increased 4105 removing a mirrored log device results in a leaked object 4106 asynchronously load metaslab Reviewed by: Matthew Ahrens <[email protected]> Reviewed by: Adam Leventhal <[email protected]> Reviewed by: Sebastien Roy <[email protected]> Approved by: Garrett D'Amore <[email protected]> Prior to this patch, space_maps were preferred solely based on the amount of free space left in each. Unfortunately, this heuristic didn't contain any information about the make-up of that free space, which meant we could keep preferring and loading a highly fragmented space map that wouldn't actually have enough contiguous space to satisfy the allocation; then unloading that space_map and repeating the process. This change modifies the space_map's to store additional information about the contiguous space in the space_map, so that we can use this information to make a better decision about which space_map to load. This requires reallocating all space_map objects to increase their bonus buffer size sizes enough to fit the new metadata. The above feature can be enabled via a new feature flag introduced by this change: com.delphix:spacemap_histogram In addition to the above, this patch allows the space_map block size to be increase. Currently the block size is set to be 4K in size, which has certain implications including the following: * 4K sector devices will not see any compression benefit * large space_maps require more metadata on-disk * large space_maps require more time to load (typically random reads) Now the space_map block size can adjust as needed up to the maximum size set via the space_map_max_blksz variable. A bug was fixed which resulted in potentially leaking an object when removing a mirrored log device. The previous logic for vdev_remove() did not deal with removing top-level vdevs that are interior vdevs (i.e. mirror) correctly. The problem would occur when removing a mirrored log device, and result in the DTL space map object being leaked; because top-level vdevs don't have DTL space map objects associated with them. References: https://www.illumos.org/issues/4101 https://www.illumos.org/issues/4102 https://www.illumos.org/issues/4103 https://www.illumos.org/issues/4105 https://www.illumos.org/issues/4106 https://github.com/illumos/illumos-gate/commit/0713e23 Porting notes: A handful of kmem_alloc() calls were converted to kmem_zalloc(). Also, the KM_PUSHPAGE and TQ_PUSHPAGE flags were used as necessary. Ported-by: Tim Chase <[email protected]> Signed-off-by: Prakash Surya <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #2488
* cstyle: Resolve C style issuesMichael Kjorling2013-12-182-11/+12
| | | | | | | | | | | | | | | | | | The vast majority of these changes are in Linux specific code. They are the result of not having an automated style checker to validate the code when it was originally written. Others were caused when the common code was slightly adjusted for Linux. This patch contains no functional changes. It only refreshes the code to conform to style guide. Everyone submitting patches for inclusion upstream should now run 'make checkstyle' and resolve any warning prior to opening a pull request. The automated builders have been updated to fail a build if when 'make checkstyle' detects an issue. Signed-off-by: Brian Behlendorf <[email protected]> Closes #1821
* Illumos #3582, #3584Adam Leventhal2013-11-041-0/+35
| | | | | | | | | | | | | | | | | | | | 3582 zfs_delay() should support a variable resolution 3584 DTrace sdt probes for ZFS txg states Reviewed by: Matthew Ahrens <[email protected]> Reviewed by: George Wilson <[email protected]> Reviewed by: Christopher Siden <[email protected]> Reviewed by: Dan McDonald <[email protected]> Reviewed by: Richard Elling <[email protected]> Approved by: Garrett D'Amore <[email protected]> References: https://www.illumos.org/issues/3582 illumos/illumos-gate@0689f76 Ported by: Ned Bass <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Issue #1775
* Illumos #3537Matthew Ahrens2013-10-311-2/+31
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 3537 want pool io kstats Reviewed by: George Wilson <[email protected]> Reviewed by: Adam Leventhal <[email protected]> Reviewed by: Eric Schrock <[email protected]> Reviewed by: Sa?o Kiselkov <[email protected]> Reviewed by: Garrett D'Amore <[email protected]> Reviewed by: Brendan Gregg <[email protected]> Approved by: Gordon Ross <[email protected]> References: http://www.illumos.org/issues/3537 illumos/illumos-gate@c3a6601 Ported by: Cyril Plisko <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Porting Notes: 1. The patch was restructured to take advantage of the existing spa statistics infrastructure. To accomplish this the kstat was moved in to spa->io_stats and the init/destroy code moved to spa_stats.c. 2. The I/O kstat was simply named <pool> which conflicted with the pool directory we had already created. Therefore it was renamed to <pool>/io 3. An update handler was added to allow the kstat to be zeroed.
* Add visibility in to cached dbufsBrian Behlendorf2013-10-251-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | Currently there is no mechanism to inspect which dbufs are being cached by the system. There are some coarse counters in arcstats by they only give a rough idea of what's being cached. This patch aims to improve the current situation by adding a new dbufs kstat. When read this new kstat will walk all cached dbufs linked in to the dbuf_hash. For each dbuf it will dump detailed information about the buffer. It will also dump additional information about the referenced arc buffer and its related dnode. This provides a more complete view in to exactly what is being cached. With this generic infrastructure in place utilities can be written to post-process the data to understand exactly how the caching is working. For example, the data could be processed to show a list of all cached dnodes and how much space they're consuming. Or a similar list could be generated based on dnode type. Many other ways to interpret the data exist based on what kinds of questions you're trying to answer. Signed-off-by: Brian Behlendorf <[email protected]> Signed-off-by: Prakash Surya <[email protected]>
* Add visibility in to arc_readPrakash Surya2013-10-252-0/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This change is an attempt to add visibility into the arc_read calls occurring on a system, in real time. To do this, a list was added to the in memory SPA data structure for a pool, with each element on the list corresponding to a call to arc_read. These entries are then exported through the kstat interface, which can then be interpreted in userspace. For each arc_read call, the following information is exported: * A unique identifier (uint64_t) * The time the entry was added to the list (hrtime_t) (*not* wall clock time; relative to the other entries on the list) * The objset ID (uint64_t) * The object number (uint64_t) * The indirection level (uint64_t) * The block ID (uint64_t) * The name of the function originating the arc_read call (char[24]) * The arc_flags from the arc_read call (uint32_t) * The PID of the reading thread (pid_t) * The command or name of thread originating read (char[16]) From this exported information one can see, in real time, exactly what is being read, what function is generating the read, and whether or not the read was found to be already cached. There is still some work to be done, but this should serve as a good starting point. Specifically, dbuf_read's are not accounted for in the currently exported information. Thus, a follow up patch should probably be added to export these calls that never call into arc_read (they only hit the dbuf hash table). In addition, it might be nice to create a utility similar to "arcstat.py" to digest the exported information and display it in a more readable format. Or perhaps, log the information and allow for it to be "replayed" at a later time. Signed-off-by: Prakash Surya <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]>
* Fix libzfs_core changes to follow GNU libtool guidelinesRichard Yao2013-10-101-1/+1
| | | | | | | | | | | | | | | | | | | | The GNU libtool documentation states to start with a version of 0:0:0, rather than 1:1:0. Illumos uses the name libzfs_core.so.1, so to be consistent, we should go with 1:0:0. http://www.gnu.org/software/libtool/manual/libtool.html#Updating-version-info The GNU libtool documentation also provides guidence on how the version information should be incremented. Doing this does a SONAME bump of the libzfs and libzpool libraries. This is particularly important on Gentoo because a SONAME bump enables portage to retain the older libraries until any packages that link to them are rebuilt. The main example of this is GRUB2's grub2-mkconfig, which will break unless it is rebuilt against the new libraries. Signed-off-by: Richard Yao <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Issue #1751
* Generate libraries with correct DT_NEEDED entriesRichard Yao2013-10-101-1/+2
| | | | | | | | | | | | | | | | | | | | Libraries that depend on other libraries should list them in ELF's DT_NEEDED field so that programs linking to them do not need to specify those libraries unless they depend on them as well. This is not the case in the current code and the consequence is that anything that needs a library must know its dependencies. This is fragile and caused GRUB2's configure script to break when a dependency was added on libblkid in libzfs. This resolves that problem by using LIBADD/LDADD to specify libraries in Makefile.am instead of LDFLAGS. This ensures that proper DT_NEEDED entries are generated and prevents GRUB2's configure script from breaking in the presence of a libblkid dependency. This also removes unneeded dependencies from various files. Signed-off-by: Richard Yao <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Issue #1751
* Illumos #3464Matthew Ahrens2013-09-042-0/+7
| | | | | | | | | | | | | | | | | 3464 zfs synctask code needs restructuring Reviewed by: Dan Kimmel <[email protected]> Reviewed by: Adam Leventhal <[email protected]> Reviewed by: George Wilson <[email protected]> Reviewed by: Christopher Siden <[email protected]> Approved by: Garrett D'Amore <[email protected]> References: https://www.illumos.org/issues/3464 illumos/illumos-gate@3b2aab18808792cbd248a12f1edf139b89833c13 Ported-by: Tim Chase <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #1495
* Illumos #2882, #2883, #2900Matthew Ahrens2013-09-041-0/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 2882 implement libzfs_core 2883 changing "canmount" property to "on" should not always remount dataset 2900 "zfs snapshot" should be able to create multiple, arbitrary snapshots at once Reviewed by: George Wilson <[email protected]> Reviewed by: Chris Siden <[email protected]> Reviewed by: Garrett D'Amore <[email protected]> Reviewed by: Bill Pijewski <[email protected]> Reviewed by: Dan Kruchinin <[email protected]> Approved by: Eric Schrock <[email protected]> References: https://www.illumos.org/issues/2882 https://www.illumos.org/issues/2883 https://www.illumos.org/issues/2900 illumos/illumos-gate@4445fffbbb1ea25fd0e9ea68b9380dd7a6709025 Ported-by: Tim Chase <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #1293 Porting notes: WARNING: This patch changes the user/kernel ABI. That means that the zfs/zpool utilities built from master are NOT compatible with the 0.6.2 kernel modules. Ensure you load the matching kernel modules from master after updating the utilities. Otherwise the zfs/zpool commands will be unable to interact with your pool and you will see errors similar to the following: $ zpool list failed to read pool configuration: bad address no pools available $ zfs list no datasets available Add zvol minor device creation to the new zfs_snapshot_nvl function. Remove the logging of the "release" operation in dsl_dataset_user_release_sync(). The logging caused a null dereference because ds->ds_dir is zeroed in dsl_dataset_destroy_sync() and the logging functions try to get the ds name via the dsl_dataset_name() function. I've got no idea why this particular code would have worked in Illumos. This code has subsequently been completely reworked in Illumos commit 3b2aab1 (3464 zfs synctask code needs restructuring). Squash some "may be used uninitialized" warning/erorrs. Fix some printf format warnings for %lld and %llu. Apply a few spa_writeable() changes that were made to Illumos in illumos/illumos-gate.git@cd1c8b8 as part of the 3112, 3113, 3114 and 3115 fixes. Add a missing call to fnvlist_free(nvl) in log_internal() that was added in Illumos to fix issue 3085 but couldn't be ported to ZoL at the time (zfsonlinux/zfs@9e11c73) because it depended on future work.
* Use taskq for dump_bytes()Brian Behlendorf2013-05-061-0/+6
| | | | | | | | | | | | | | | | | | | The vn_rdwr() function performs I/O by calling the vfs_write() or vfs_read() functions. These functions reside just below the system call layer and the expectation is they have almost the entire 8k of stack space to work with. In fact, certain layered configurations such as ext+lvm+md+multipath require the majority of this stack to avoid stack overflows. To avoid this posibility the vn_rdwr() call in dump_bytes() has been moved to the ZIO_TYPE_FREE, taskq. This ensures that all I/O will be performed with the majority of the stack space available. This ends up being very similiar to as if the I/O were issued via sys_write() or sys_read(). Signed-off-by: Brian Behlendorf <[email protected]> Closes #1399 Closes #1423
* Silence 'old_umask' uninit variable warningBrian Behlendorf2013-05-011-1/+1
| | | | | | | | | | | | Recent changes have caused older versions of gcc to mistakenly flag 'old_umask' in vn_open() as an unitialized variable. To silence the warning initialize it. kernel.c: In function 'vn_open': kernel.c:525:6: error: 'old_umask' may be used uninitialized in this function Signed-off-by: Brian Behlendorf <[email protected]>
* 3246 ZFS I/O deadman threadGeorge.Wilson2013-05-011-0/+13
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Reviewed by: Matt Ahrens <[email protected]> Reviewed by: Eric Schrock <[email protected]> Reviewed by: Christopher Siden <[email protected]> Approved by: Garrett D'Amore <[email protected]> NOTES: This patch has been reworked from the original in the following ways to accomidate Linux ZFS implementation *) Usage of the cyclic interface was replaced by the delayed taskq interface. This avoids the need to implement new compatibility code and allows us to rely on the existing taskq implementation. *) An extern for zfs_txg_synctime_ms was added to sys/dsl_pool.h because declaring externs in source files as was done in the original patch is just plain wrong. *) Instead of panicing the system when the deadman triggers a zevent describing the blocked vdev and the first pending I/O is posted. If the panic behavior is desired Linux provides other generic methods to panic the system when threads are observed to hang. *) For reference, to delay zios by 30 seconds for testing you can use zinject as follows: 'zinject -d <vdev> -D30 <pool>' References: illumos/illumos-gate@283b84606b6fc326692c03273de1774e8c122f9a https://www.illumos.org/issues/3246 Ported-by: Brian Behlendorf <[email protected]> Closes #1396
* Fix function relocations in libzpoolRichard Yao2013-02-051-1/+2
| | | | | | | | | | | binutils 2.23.1 fails in situations that generate function relocations on PowerPC and possibly other architectures. This causes linking of libzpool to fail because it depends on libnvpair. We add a dependency on libnvpair to lib/libzpool/Makefile.am to correct that. Signed-off-by: Richard Yao <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #1267
* Remove NPTL_GUARD_WITHIN_STACKBrian Behlendorf2013-01-291-2/+1
| | | | | | | | | | | | | | | | | Commit 4b2f65b253952c5103311cc8bb4b8cdc6836fd7e increased the user space stack by 4x to resolve certain stack overflows. As such it no longer makes sense to worry about a single extra page which might or might not be part of the process stack. There is now ample headroom for normal usage. By eliminating this configure check we are also resolving the following segfault which intentionally occurs at configure time and may be logged in dmesg. conftest[22156]: segfault at 7fbf18a47e48 ip 00000000004007fe sp 00007fbf18a4be50 error 6 in conftest[400000+1000] Signed-off-by: Brian Behlendorf <[email protected]>
* Illumos #3035 LZ4 compression support in ZFS and GRUBEric Dillmann2013-01-291-0/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 3035 LZ4 compression support in ZFS and GRUB Reviewed by: Matthew Ahrens <[email protected]> Reviewed by: Christopher Siden <[email protected]> Reviewed by: George Wilson <[email protected]> Approved by: Christopher Siden <[email protected]> References: illumos/illumos-gate@a6f561b4aee75d0d028e7b36b151c8ed8a86bc76 https://www.illumos.org/issues/3035 http://wiki.illumos.org/display/illumos/LZ4+Compression+In+ZFS This patch has been slightly modified from the upstream Illumos version to be compatible with Linux. Due to the very limited stack space in the kernel a lz4 workspace kmem cache is used. Since we are using gcc we are also able to take advantage of the gcc optimized __builtin_ctz functions. Support for GRUB has been dropped from this patch. That code is available but those changes will need to made to the upstream GRUB package. Lastly, several hunks of dead code were dropped for clarity. They include the functions real_LZ4_uncompress(), LZ4_compressBound() and the Visual Studio specific hunks wrapped in _MSC_VER. Ported-by: Eric Dillmann <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #1217
* Illumos #1557 assertion failed in userland taskq_destroy()Garrett D'Amore2013-01-111-3/+2
| | | | | | | | | | | | | | | 1557 assertion failed in userland taskq_destroy() Reviewed by: Richard Lowe <[email protected]> Reviewed by: George Wilson <[email protected]> Approved by: Eric Schrock <[email protected]> References: illumos/illumos-gate@aa846ad9bc4785806bb6263657698d5890afbc08 illumos changeset: 13597:3eac1e8e0f4c https://www.illumos.org/issues/1557 Ported-by: Brian Behlendorf <[email protected]>
* Illumos #2619 and #2747Christopher Siden2013-01-082-1/+6
| | | | | | | | | | | | | | | | | | | | | | 2619 asynchronous destruction of ZFS file systems 2747 SPA versioning with zfs feature flags Reviewed by: Matt Ahrens <[email protected]> Reviewed by: George Wilson <[email protected]> Reviewed by: Richard Lowe <[email protected]> Reviewed by: Dan Kruchinin <[email protected]> Approved by: Eric Schrock <[email protected]> References: illumos/illumos-gate@53089ab7c84db6fb76c16ca50076c147cda11757 illumos/illumos-gate@ad135b5d644628e791c3188a6ecbd9c257961ef8 illumos changeset: 13700:2889e2596bd6 https://www.illumos.org/issues/2619 https://www.illumos.org/issues/2747 NOTE: The grub specific changes were not ported. This change must be made to the Linux grub packages. Ported-by: Brian Behlendorf <[email protected]>
* Create threads in detached state in userspace.Etienne Dechamps2012-10-031-1/+2
| | | | | | | | | | | | | | | | | | | | | Currently, thread_create(), when called in userspace, creates a joinable (i.e. not detached thread). This is the pthread default. Unfortunately, this does not reproduce kthreads behavior (kthreads are always detached). In addition, this contradicts the original Solaris code which creates userspace threads in detached mode. These joinable threads are never joined, which leads to a leakage of pthread thread objects ("zombie threads"). This in turn results in excessive ressource consumption, and possible ressource exhaustion in extreme cases (e.g. long ztest runs). This patch fixes the issue by creating userspace threads in detached mode. The only exception is ztest worker threads which are meant to be joinable. Signed-off-by: Brian Behlendorf <[email protected]> Issue #989
* Increase the stack space in userspace.Etienne Dechamps2012-09-061-4/+9
| | | | | | | | | | | | | | | | | | In 1e33ac1e2677c898a0b5ef6207048c692cb51bf4, the maximum stack size for userspace tools was set to 8k to mimic the available kernel stack size. Unfortunately, due to differences in how the stack is used in userspace vs kernel space, spurious stack overflows could occur in userspace tools due to the limited stack size. This is especially true in ztest when debugging is enabled. This patch multiplies the userspace stack size by 4, which fixes the stack overflow issues. This comes at the price of not being able to catch stack size issues in userspace, but the previous solution proved unreliable anyway. Signed-off-by: Brian Behlendorf <[email protected]> Fixes #934.
* Remove autotools productsBrian Behlendorf2012-08-271-1497/+0
| | | | | | | | Remove all of the generated autotools products from the repository and update the .gitignore files accordingly. Signed-off-by: Brian Behlendorf <[email protected]> Closes #718
* Set zvol discard_granularity to the volblocksize.Etienne Dechamps2012-08-071-0/+1
| | | | | | | | | | | | | | | | | | Currently, zvols have a discard granularity set to 0, which suggests to the upper layer that discard requests of arbirarily small size and alignment can be made efficiently. In practice however, ZFS does not handle unaligned discard requests efficiently: indeed, it is unable to free a part of a block. It will write zeros to the specified range instead, which is both useless and inefficient (see dnode_free_range). With this patch, zvol block devices expose volblocksize as their discard granularity, so the upper layer is aware that it's not supposed to send discard requests smaller than volblocksize. Signed-off-by: Brian Behlendorf <[email protected]> Closes #862
* Linux 3.5 compat, end_writeback() changed to clear_inode()Richard Yao2012-07-231-0/+1
| | | | | | | | | | | | | | | | The end_writeback() function was changed by moving the call to inode_sync_wait() earlier in to evict(). This effecitvely changes the ordering of the sync but it does not impact the details of the zfs implementation. However, as part of this change end_writeback() was renamed to clear_inode() to reflect the new semantics. This change does impact us and clear_inode() now maps to end_writeback() for kernels prior to 3.5. Signed-off-by: Richard Yao <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #784
* Linux 3.5 compat, iops->truncate_range() removedRichard Yao2012-07-231-0/+1
| | | | | | | | | The vmtruncate_range() support has been removed from the kernel in favor of using the fallocate method in the file_operations table. Signed-off-by: Richard Yao <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Issue #784
* Linux 3.5 compat, eops->encode_fh() takes inodesRichard Yao2012-07-231-0/+1
| | | | | | | | | | | | | | The export_operations member ->encode_fh() has been updated to take both the child and parent inodes. This interface used to take the child dentry and a bool describing if the parent is needed. NOTE: While updating this code I noticed that we do not currently cleanly handle the case where we're passed a connectable parent. This code should be audited to make sure we're doing the right thing. Signed-off-by: Richard Yao <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Issue #784
* Move partition scanning from userspace to module.Etienne Dechamps2012-07-171-0/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, zpool online -e (dynamic vdev expansion) doesn't work on whole disks because we're invoking ioctl(BLKRRPART) from userspace while ZFS still has a partition open on the disk, which results in EBUSY. This patch moves the BLKRRPART invocation from the zpool utility to the module. Specifically, this is done just before opening the device in vdev_disk_open() which is called inside vdev_reopen(). This requires jumping through some hoops to get to the disk device from the partition device, and to make sure we can still open the partition after the BLKRRPART call. Note that this new code path is triggered on dynamic vdev expansion only; other actions, like creating a new pool, are unchanged and still call BLKRRPART from userspace. This change also depends on API changes which are available in 2.6.37 and latter kernels. The build system has been updated to detect this, but there is no compatibility mode for older kernels. This means that online expansion will NOT be available in older kernels. However, it will still be possible to expand the vdev offline. Signed-off-by: Brian Behlendorf <[email protected]> Closes #808
* Linux 3.4 compat, d_make_root() replaces d_alloc_root()Richard Yao2012-06-111-0/+1
| | | | | | | | | | | | | | | | | | | | torvalds/linux@adc0e91ab142abe93f5b0d7980ada8a7676231fe introduced introduced d_make_root() as a replacement for d_alloc_root(). Further commits appear to have removed d_alloc_root() from the Linux source tree. This causes the following failure: error: implicit declaration of function 'd_alloc_root' [-Werror=implicit-function-declaration] To correct this we update the code to use the current d_make_root() interface for readability. Then we introduce an autotools check to determine if d_make_root() is available. If it isn't then we define some compatibility logic which used the older d_alloc_root() interface. Signed-off-by: Richard Yao <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #776
* Linux 3.3 compat, iops->create()/mkdir()/mknod()Brian Behlendorf2012-04-301-0/+1
| | | | | | | | | | The mode argument of iops->create()/mkdir()/mknod() was changed from an 'int' to a 'umode_t'. To prevent a compiler warning an autoconf check was added to detect the API change and then correctly set a zpl_umode_t typedef. There is no functional change. Signed-off-by: Brian Behlendorf <[email protected]> Closes #701
* Add --enable-debug-dmu-tx configure optionBrian Behlendorf2012-03-231-0/+1
| | | | | | | | | | | | | | | | | | Allow rigorous (and expensive) tx validation to be enabled/disabled indepentantly from the standard zfs debugging. When enabled these checks ensure that all txs are constructed properly and that a dbuf is never dirtied without taking the correct tx hold. This checking is particularly helpful when adding new dmu consumers like Lustre. However, for established consumers such as the zpl with no known outstanding tx construction problems this is just overhead. --enable-debug-dmu-tx - Enable/disable validation of each tx as --disable-debug-dmu-tx it is constructed. By default validation is disabled due to performance concerns. Signed-off-by: Brian Behlendorf <[email protected]>
* Add .zfs control directoryBrian Behlendorf2012-03-222-0/+5
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Add support for the .zfs control directory. This was accomplished by leveraging as much of the existing ZFS infrastructure as posible and updating it for Linux as required. The bulk of the core functionality is now all there with the following limitations. *) The .zfs/snapshot directory automount support requires a 2.6.37 or newer kernel. The exception is RHEL6.2 which has backported the d_automount patches. *) Creating/destroying/renaming snapshots with mkdir/rmdir/mv in the .zfs/snapshot directory works as expected. However, this functionality is only available to root until zfs delegations are finished. * mkdir - create a snapshot * rmdir - destroy a snapshot * mv - rename a snapshot The following issues are known defeciences, but we expect them to be addressed by future commits. *) Add automount support for kernels older the 2.6.37. This should be possible using follow_link() which is what Linux did before. *) Accessing the .zfs/snapshot directory via NFS is not yet possible. The majority of the ground work for this is complete. However, finishing this work will require resolving some lingering integration issues with the Linux NFS kernel server. *) The .zfs/shares directory exists but no futher smb functionality has yet been implemented. Contributions-by: Rohan Puri <[email protected]> Contributiobs-by: Andrew Barnes <[email protected]> Signed-off-by: Brian Behlendorf <[email protected]> Closes #173
* Cleanly support debug packagesBrian Behlendorf2012-02-271-0/+1
| | | | | | | | | | | | | | | | | | | Allow a source rpm to be rebuilt with debugging enabled. This avoids the need to have to manually modify the spec file. By default debugging is still largely disabled. To enable specific debugging features use the following options with rpmbuild. '--with debug' - Enables ASSERTs # For example: $ rpmbuild --rebuild --with debug zfs-modules-0.6.0-rc6.src.rpm Additionally, ZFS_CONFIG has been added to zfs_config.h for packages which build against these headers. This is critical to ensure both zfs and the dependant package are using the same prototype and structure definitions. Signed-off-by: Brian Behlendorf <[email protected]>
* Add support for DISCARD to ZVOLs.Etienne Dechamps2012-02-091-0/+1
| | | | | | | | | | | | | | | | | | | | DISCARD (REQ_DISCARD, BLKDISCARD) is useful for thin provisioning. It allows ZVOL clients to discard (unmap, trim) block ranges from a ZVOL, thus optimizing disk space usage by allowing a ZVOL to shrink instead of just grow. We can't use zfs_space() or zfs_freesp() here, since these functions only work on regular files, not volumes. Fortunately we can use the low-level function dmu_free_long_range() which does exactly what we want. Currently the discard operation is not added to the log. That's not a big deal since losing discard requests cannot result in data corruption. It would however result in disk space usage higher than it should be. Thus adding log support to zvol_discard() is probably a good idea for a future improvement. Signed-off-by: Brian Behlendorf <[email protected]>
* Support the fallocate() file operation.Etienne Dechamps2012-02-091-0/+1
| | | | | | | | | | | | | | Currently only the (FALLOC_FL_PUNCH_HOLE) flag combination is supported, since it's the only one that matches the behavior of zfs_space(). This makes it pretty much useless in its current form, but it's a start. To support other flag combinations we would need to modify zfs_space() to make it more flexible, or emulate the desired functionality in zpl_fallocate(). Signed-off-by: Brian Behlendorf <[email protected]> Issue #334
* Improve ZVOL queue behavior.Etienne Dechamps2012-02-071-0/+5
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The Linux block device queue subsystem exposes a number of configurable settings described in Linux block/blk-settings.c. The defaults for these settings are tuned for hard drives, and are not optimized for ZVOLs. Proper configuration of these options would allow upper layers (I/O scheduler) to take better decisions about write merging and ordering. Detailed rationale: - max_hw_sectors is set to unlimited (UINT_MAX). zvol_write() is able to handle writes of any size, so there's no reason to impose a limit. Let the upper layer decide. - max_segments and max_segment_size are set to unlimited. zvol_write() will copy the requests' contents into a dbuf anyway, so the number and size of the segments are irrelevant. Let the upper layer decide. - physical_block_size and io_opt are set to the ZVOL's block size. This has the potential to somewhat alleviate issue #361 for ZVOLs, by warning the upper layers that writes smaller than the volume's block size will be slow. - The NONROT flag is set to indicate this isn't a rotational device. Although the backing zpool might be composed of rotational devices, the resulting ZVOL often doesn't exhibit the same behavior due to the COW mechanisms used by ZFS. Setting this flag will prevent upper layers from making useless decisions (such as reordering writes) based on incorrect assumptions about the behavior of the ZVOL. Signed-off-by: Brian Behlendorf <[email protected]>
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