Fix ARC behavior on 32-bit systems

With the addition of the ABD changes consumption of the virtual
address space has been greatly reduced.  This exposed an issue on
CONFIG_HIGHMEM systems where free memory was being calculated
incorrectly.  Functionally this didn't cause any major problems
prior to ABD because a lack of available virtual address space
was used as an indicator of low memory.

This patch makes the following changes to address the issue and
in the process realigns the code further with OpenZFS.  There
are no substantive changes in behavior for 64-bit systems.

* Added CONFIG_HIGHMEM case to the arc_all_memory() and
  arc_free_memory() functions to only consider low memory pages
  on CONFIG_HIGHMEM systems.

* The arc_free_memory() function was updated to return bytes
  instead of pages to be consistent with the other helper
  functions.  In user space we make up some reasonable values
  since currently only testing is performed in this context.

* Adds three new values to the arcstats kstat to provide visibility
  in to the ARC's assessment of the memory situation:
  memory_all_bytes, memory_free_bytes, and memory_available_bytes.

* Added kmem_reap() call to arc_available_memory() for 32-bit
  builds to realign code with OpenZFS.

* Reduced size of test file in /async_destroy_001_pos.ksh to
  speed up test case.  Multiple txgs are still required.

* Move vdevs used by zpool_clear_001_pos and zpool_upgrade_002_pos
  to TEST_BASE_DIR location to speed up test cases.

Reviewed-by: David Quigley <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #5352
Closes #6734

1 files changed, 58 insertions, 27 deletions

diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index 3230a3d2e..992e57ce6 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -649,6 +649,9 @@ typedef struct arc_stats {
 	kstat_named_t arcstat_memory_throttle_count;
 	kstat_named_t arcstat_memory_direct_count;
 	kstat_named_t arcstat_memory_indirect_count;
+	kstat_named_t arcstat_memory_all_bytes;
+	kstat_named_t arcstat_memory_free_bytes;
+	kstat_named_t arcstat_memory_available_bytes;
 	kstat_named_t arcstat_no_grow;
 	kstat_named_t arcstat_tempreserve;
 	kstat_named_t arcstat_loaned_bytes;
@@ -745,6 +748,9 @@ static arc_stats_t arc_stats = {
 	{ "memory_throttle_count",	KSTAT_DATA_UINT64 },
 	{ "memory_direct_count",	KSTAT_DATA_UINT64 },
 	{ "memory_indirect_count",	KSTAT_DATA_UINT64 },
+	{ "memory_all_bytes",		KSTAT_DATA_UINT64 },
+	{ "memory_free_bytes",		KSTAT_DATA_UINT64 },
+	{ "memory_available_bytes",	KSTAT_DATA_INT64 },
 	{ "arc_no_grow",		KSTAT_DATA_UINT64 },
 	{ "arc_tempreserve",		KSTAT_DATA_UINT64 },
 	{ "arc_loaned_bytes",		KSTAT_DATA_UINT64 },
@@ -4658,30 +4664,46 @@ static uint64_t
 arc_all_memory(void)
 {
 #ifdef _KERNEL
-	return (MIN(ptob(physmem),
-	    vmem_size(heap_arena, VMEM_FREE | VMEM_ALLOC)));
+#ifdef CONFIG_HIGHMEM
+	return (ptob(totalram_pages - totalhigh_pages));
+#else
+	return (ptob(totalram_pages));
+#endif /* CONFIG_HIGHMEM */
 #else
 	return (ptob(physmem) / 2);
-#endif
+#endif /* _KERNEL */
 }
 
-#ifdef _KERNEL
+/*
+ * Return the amount of memory that is considered free.  In user space
+ * which is primarily used for testing we pretend that free memory ranges
+ * from 0-20% of all memory.
+ */
 static uint64_t
 arc_free_memory(void)
 {
+#ifdef _KERNEL
+#ifdef CONFIG_HIGHMEM
+	struct sysinfo si;
+	si_meminfo(&si);
+	return (ptob(si.freeram - si.freehigh));
+#else
 #ifdef ZFS_GLOBAL_NODE_PAGE_STATE
-	return (nr_free_pages() +
+	return (ptob(nr_free_pages() +
 	    global_node_page_state(NR_INACTIVE_FILE) +
 	    global_node_page_state(NR_INACTIVE_ANON) +
-	    global_node_page_state(NR_SLAB_RECLAIMABLE));
+	    global_node_page_state(NR_SLAB_RECLAIMABLE)));
 #else
-	return (nr_free_pages() +
+	return (ptob(nr_free_pages() +
 	    global_page_state(NR_INACTIVE_FILE) +
 	    global_page_state(NR_INACTIVE_ANON) +
-	    global_page_state(NR_SLAB_RECLAIMABLE));
-#endif
+	    global_page_state(NR_SLAB_RECLAIMABLE)));
+#endif /* ZFS_GLOBAL_NODE_PAGE_STATE */
+#endif /* CONFIG_HIGHMEM */
+#else
+	return (spa_get_random(arc_all_memory() * 20 / 100));
+#endif /* _KERNEL */
 }
-#endif
 
 typedef enum free_memory_reason_t {
 	FMR_UNKNOWN,
@@ -4719,17 +4741,15 @@ arc_available_memory(void)
 	int64_t lowest = INT64_MAX;
 	free_memory_reason_t r = FMR_UNKNOWN;
 #ifdef _KERNEL
-	uint64_t available_memory = ptob(arc_free_memory());
 	int64_t n;
 #ifdef __linux__
+#ifdef freemem
+#undef freemem
+#endif
 	pgcnt_t needfree = btop(arc_need_free);
 	pgcnt_t lotsfree = btop(arc_sys_free);
 	pgcnt_t desfree = 0;
-#endif
-
-#if defined(__i386)
-	available_memory =
-	    MIN(available_memory, vmem_size(heap_arena, VMEM_FREE));
+	pgcnt_t freemem = btop(arc_free_memory());
 #endif
 
 	if (needfree > 0) {
@@ -4747,7 +4767,7 @@ arc_available_memory(void)
 	 * number of needed free pages.  We add extra pages here to make sure
 	 * the scanner doesn't start up while we're freeing memory.
 	 */
-	n = PAGESIZE * (btop(available_memory) - lotsfree - needfree - desfree);
+	n = PAGESIZE * (freemem - lotsfree - needfree - desfree);
 	if (n < lowest) {
 		lowest = n;
 		r = FMR_LOTSFREE;
@@ -4768,7 +4788,6 @@ arc_available_memory(void)
 		r = FMR_SWAPFS_MINFREE;
 	}
 
-
 	/*
 	 * Check that we have enough availrmem that memory locking (e.g., via
 	 * mlock(3C) or memcntl(2)) can still succeed.  (pages_pp_maximum
@@ -4784,9 +4803,9 @@ arc_available_memory(void)
 	}
 #endif
 
-#if defined(__i386)
+#if defined(_ILP32)
 	/*
-	 * If we're on an i386 platform, it's possible that we'll exhaust the
+	 * If we're on a 32-bit platform, it's possible that we'll exhaust the
 	 * kernel heap space before we ever run out of available physical
 	 * memory.  Most checks of the size of the heap_area compare against
 	 * tune.t_minarmem, which is the minimum available real memory that we
@@ -4855,6 +4874,7 @@ arc_kmem_reap_now(void)
 	extern kmem_cache_t	*zio_data_buf_cache[];
 	extern kmem_cache_t	*range_seg_cache;
 
+#ifdef _KERNEL
 	if ((arc_meta_used >= arc_meta_limit) && zfs_arc_meta_prune) {
 		/*
 		 * We are exceeding our meta-data cache limit.
@@ -4862,9 +4882,16 @@ arc_kmem_reap_now(void)
 		 */
 		arc_prune_async(zfs_arc_meta_prune);
 	}
+#if defined(_ILP32)
+	/*
+	 * Reclaim unused memory from all kmem caches.
+	 */
+	kmem_reap();
+#endif
+#endif
 
 	for (i = 0; i < SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT; i++) {
-#ifdef _ILP32
+#if defined(_ILP32)
 		/* reach upper limit of cache size on 32-bit */
 		if (zio_buf_cache[i] == NULL)
 			break;
@@ -6922,14 +6949,11 @@ static int
 arc_memory_throttle(uint64_t reserve, uint64_t txg)
 {
 #ifdef _KERNEL
-	uint64_t available_memory = ptob(arc_free_memory());
+	uint64_t available_memory = arc_free_memory();
 	static uint64_t page_load = 0;
 	static uint64_t last_txg = 0;
-#ifdef __linux__
-	pgcnt_t minfree = btop(arc_sys_free / 4);
-#endif
 
-#if defined(__i386)
+#if defined(_ILP32)
 	available_memory =
 	    MIN(available_memory, vmem_size(heap_arena, VMEM_FREE));
 #endif
@@ -6947,7 +6971,7 @@ arc_memory_throttle(uint64_t reserve, uint64_t txg)
 	 * continue to let page writes occur as quickly as possible.
 	 */
 	if (current_is_kswapd()) {
-		if (page_load > MAX(ptob(minfree), available_memory) / 4) {
+		if (page_load > MAX(arc_sys_free / 4, available_memory) / 4) {
 			DMU_TX_STAT_BUMP(dmu_tx_memory_reclaim);
 			return (SET_ERROR(ERESTART));
 		}
@@ -7077,6 +7101,13 @@ arc_kstat_update(kstat_t *ksp, int rw)
 		    &as->arcstat_mfu_ghost_size,
 		    &as->arcstat_mfu_ghost_evictable_data,
 		    &as->arcstat_mfu_ghost_evictable_metadata);
+
+		as->arcstat_memory_all_bytes.value.ui64 =
+		    arc_all_memory();
+		as->arcstat_memory_free_bytes.value.ui64 =
+		    arc_free_memory();
+		as->arcstat_memory_available_bytes.value.i64 =
+		    arc_available_memory();
 	}
 
 	return (0);