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mm, slab: faster active and free stats

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Reading /proc/slabinfo or monitoring slabtop(1) can become very
expensive if there are many slab caches and if there are very lengthy
per-node partial and/or free lists.

Commit 07a63c41fa ("mm/slab: improve performance of gathering slabinfo
stats") addressed the per-node full lists which showed a significant
improvement when no objects were freed.  This patch has the same
motivation and optimizes the remainder of the usecases where there are
very lengthy partial and free lists.

This patch maintains per-node active_slabs (full and partial) and
free_slabs rather than iterating the lists at runtime when reading
/proc/slabinfo.

When allocating 100GB of slab from a test cache where every slab page is
on the partial list, reading /proc/slabinfo (includes all other slab
caches on the system) takes ~247ms on average with 48 samples.

As a result of this patch, the same read takes ~0.856ms on average.

[[email protected]: changelog]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Greg Thelen <[email protected]>
Signed-off-by: David Rientjes <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Greg Thelen 2016-12-12 16:41:41 -08:00 • committed by Linus Torvalds
commit f728b0a5d7
2 changed files with 49 additions and 71 deletions
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mm/slab.h
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@ -447,7 +447,8 @@ struct kmem_cache_node {
struct list_head slabs_partial; /* partial list first, better asm code */
struct list_head slabs_full;
struct list_head slabs_free;
unsigned long num_slabs;
unsigned long active_slabs; /* length of slabs_partial+slabs_full */
unsigned long free_slabs; /* length of slabs_free */
unsigned long free_objects;
unsigned int free_limit;
unsigned int colour_next; /* Per-node cache coloring */