On Wed, Jun 11, 2008 at 04:09:47PM -0400, Jeff Layton wrote: > On Wed, 11 Jun 2008 15:52:22 -0400 > "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote: > > > I'm probably missing something fundamental--why doesn't > > /proc/slab_allocators show any results for size-x where x >= 4096? > > > > Someone's seeing a performance problem with the linux nfs server. One > > of the symptoms is the "size-4096" slab cache seems to be out of > > control. I assumed that meant that memory allocated by kmalloc() might > > be leaking, so figured it might be interesting to turn on > > CONFIG_DEBUG_SLAB_LEAK. As far as I can tell what that does is list > > kmalloc() callers in /proc/slab_allocators. But that doesn't seem to be > > showing any results for size-4096. Can anyone provide a clue? > > Thanks! > > > > --b. > > > > > Hmm...I've never used this, but in kmem_cache_alloc(): > > /* > * Enable redzoning and last user accounting, except for caches with > * large objects, if the increased size would increase the object size > * above the next power of two: caches with object sizes just above a > * power of two have a significant amount of internal fragmentation. > */ > if (size < 4096 || fls(size - 1) == fls(size-1 + REDZONE_ALIGN + > 2 * sizeof(unsigned long long))) > flags |= SLAB_RED_ZONE | SLAB_STORE_USER; > > > ...looks like it specifically excludes some caches. Ah, I missed that! I'm a little confused as to how those flags behavior affect the collection of the leak debugging data, but I can verify that the below does result in size-4096 showing up in /proc/slab_allocators; hopefully there's no more negative result than the performance penalty. Norman, do you think you could try applying this and then trying again? --b. diff --git a/mm/slab.c b/mm/slab.c index 06236e4..b379e31 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -2202,7 +2202,7 @@ kmem_cache_create (const char *name, size_t size, size_t align, * above the next power of two: caches with object sizes just above a * power of two have a significant amount of internal fragmentation. */ - if (size < 4096 || fls(size - 1) == fls(size-1 + REDZONE_ALIGN + + if (size < 8192 || fls(size - 1) == fls(size-1 + REDZONE_ALIGN + 2 * sizeof(unsigned long long))) flags |= SLAB_RED_ZONE | SLAB_STORE_USER; if (!(flags & SLAB_DESTROY_BY_RCU)) -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
