slub: add slab with one free object to partial list tail
authorShaohua Li <shaohua.li@intel.com>
Tue, 23 Aug 2011 00:36:59 +0000 (08:36 +0800)
committerPekka Enberg <penberg@kernel.org>
Sat, 27 Aug 2011 08:58:59 +0000 (11:58 +0300)
commit130655ef097940b627e8e04fa7c6f3b51cf24f85
treec5b968196fe7f7ffcbe9def5dc70dc413a318dbd
parent81107188f123e3c2217ac2f2feb2a1147904c62f
slub: add slab with one free object to partial list tail

The slab has just one free object, adding it to partial list head doesn't make
sense. And it can cause lock contentation. For example,
1. CPU takes the slab from partial list
2. fetch an object
3. switch to another slab
4. free an object, then the slab is added to partial list again
In this way n->list_lock will be heavily contended.
In fact, Alex had a hackbench regression. 3.1-rc1 performance drops about 70%
against 3.0. This patch fixes it.

Acked-by: Christoph Lameter <cl@linux.com>
Reported-by: Alex Shi <alex.shi@intel.com>
Signed-off-by: Shaohua Li <shli@kernel.org>
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
mm/slub.c