Refactor generic memory allocation interfaces

This patch achieves the following goals:

1. It replaces the preprocessor kmem flag to gfp flag mapping with
   proper translation logic. This eliminates the potential for
   surprises that were previously possible where kmem flags were
   mapped to gfp flags.

2. It maps vmem_alloc() allocations to kmem_alloc() for allocations
   sized less than or equal to the newly-added spl_kmem_alloc_max
   parameter.  This ensures that small allocations will not contend
   on a single global lock, large allocations can still be handled,
   and potentially limited virtual address space will not be squandered.
   This behavior is entirely different than under Illumos due to
   different memory management strategies employed by the respective
   kernels.  However, this functionally provides the semantics required.

3. The --disable-debug-kmem, --enable-debug-kmem (default), and
   --enable-debug-kmem-tracking allocators have been unified in to
   a single spl_kmem_alloc_impl() allocation function.  This was
   done to simplify the code and make it more maintainable.

4. Improve portability by exposing an implementation of the memory
   allocations functions that can be safely used in the same way
   they are used on Illumos.   Specifically, callers may safely
   use KM_SLEEP in contexts which perform filesystem IO.  This
   allows us to eliminate an entire class of Linux specific changes
   which were previously required to avoid deadlocking the system.

This change will be largely transparent to existing callers but there
are a few caveats:

1. Because the headers were refactored and extraneous includes removed
   callers may find they need to explicitly add additional #includes.
   In particular, kmem_cache.h must now be explicitly includes to
   access the SPL's kmem cache implementation.  This behavior is
   different from Illumos but it was done to avoid always masking
   the Linux slab functions when kmem.h is included.

2. Callers, like Lustre, which made assumptions about the definitions
   of KM_SLEEP, KM_NOSLEEP, and KM_PUSHPAGE will need to be updated.
   Other callers such as ZFS which did not will not require changes.

3. KM_PUSHPAGE is no longer overloaded to imply GFP_NOIO.  It retains
   its original meaning of allowing allocations to access reserved
   memory.  KM_PUSHPAGE callers can be converted back to KM_SLEEP.

4. The KM_NODEBUG flags has been retired and the default warning
   threshold increased to 32k.

5. The kmem_virt() functions has been removed.  For callers which
   need to distinguish between a physical and virtual address use
   is_vmalloc_addr().

Signed-off-by: Brian Behlendorf <[email protected]>

1 files changed, 40 insertions, 0 deletions

diff --git a/man/man5/spl-module-parameters.5 b/man/man5/spl-module-parameters.5
index 33e10b53c..2ec5b668e 100644
--- a/man/man5/spl-module-parameters.5
+++ b/man/man5/spl-module-parameters.5
@@ -83,6 +83,46 @@ Default value: \fB0\fR.
 .sp
 .ne 2
 .na
+\fBspl_kmem_alloc_warn\fR (uint)
+.ad
+.RS 12n
+As a general rule kmem_alloc() allocations should be small, preferably
+just a few pages since they must by physically contiguous.  Therefore, a
+rate limited warning will be printed to the console for any kmem_alloc()
+which exceeds a reasonable threshold.
+
+The default warning threshold is set to eight pages but capped at 32K to
+accommodate systems using large pages.  This value was selected to be small
+enough to ensure the largest allocations are quickly noticed and fixed.
+But large enough to avoid logging any warnings when a allocation size is
+larger than optimal but not a serious concern.  Since this value is tunable,
+developers are encouraged to set it lower when testing so any new largish
+allocations are quickly caught.  These warnings may be disabled by setting
+the threshold to zero.
+.sp
+Default value: \fB32K\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBspl_kmem_alloc_max\fR (uint)
+.ad
+.RS 12n
+Large kmem_alloc() allocations will fail if they exceed KMALLOC_MAX_SIZE.
+Allocations which are marginally smaller than this limit may succeed but
+should still be avoided due to the expense of locating a contiguous range
+of free pages.  Therefore, a maximum kmem size with reasonable safely
+margin of 4x is set.  Kmem_alloc() allocations larger than this maximum
+will quickly fail.  Vmem_alloc() allocations less than or equal to this
+value will use kmalloc(), but shift to vmalloc() when exceeding this value.
+.sp
+Default value: \fBKMALLOC_MAX_SIZE/4\fR.
+.RE
+
+.sp
+.ne 2
+.na
 \fBspl_hostid\fR (ulong)
 .ad
 .RS 12n