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SubjectRe: hackbench regression since 2.6.25-rc
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On Fri, 2008-03-14 at 17:15 -0700, Christoph Lameter wrote:
> Here is a patch to just not perform refills but switch slabs instead.
> Could check what effect doing so has on the statistics you see on the 16p?
>
> ---
> mm/slub.c | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c 2008-03-14 16:49:36.000000000 -0700
> +++ linux-2.6/mm/slub.c 2008-03-14 16:50:04.000000000 -0700
> @@ -1474,10 +1474,7 @@ static void *__slab_alloc(struct kmem_ca
> goto new_slab;
>
> slab_lock(c->page);
> - if (unlikely(!node_match(c, node)))
> - goto another_slab;
> -
> - stat(c, ALLOC_REFILL);
> + goto another_slab;
>
> load_freelist:
> object = c->page->freelist;
There is no much help. In 2.6.25-rc5, REFILL means refill from c->page->freelist
and another_slab. It's looks like its definition is confusing. In the case of
hackbench, mostly, c->page->freelist is NULL.

With #hackbench 100 process 2000, 100*20*2 (totoally 4000) processes are started.
vmstat shows about 300~500 processes are at RUNNING state, so every processor runqueue
has more than 20 processes running on 16p tigerton.


Below is the data with kernel 2.6.25-rc5+your_patch.

[ymzhang@lkp-tt01-x8664 ~]$ slabinfo kmalloc-512

Slabcache: kmalloc-512 Aliases: 1 Order : 0 Objects: 352

Sizes (bytes) Slabs Debug Memory
------------------------------------------------------------------------
Object : 512 Total : 56 Sanity Checks : Off Total: 229376
SlabObj: 512 Full : 36 Redzoning : Off Used : 180224
SlabSiz: 4096 Partial: 4 Poisoning : Off Loss : 49152
Loss : 0 CpuSlab: 16 Tracking : Off Lalig: 0
Align : 8 Objects: 8 Tracing : Off Lpadd: 0

kmalloc-512 has no kmem_cache operations

kmalloc-512: Kernel object allocation
-----------------------------------------------------------------------
No Data

kmalloc-512: Kernel object freeing
------------------------------------------------------------------------
No Data

kmalloc-512: No NUMA information available.

Slab Perf Counter Alloc Free %Al %Fr
--------------------------------------------------
Fastpath 55883575 6130576 69 7
Slowpath 24131134 73883818 30 92
Page Alloc 84844 84788 0 0
Add partial 270625 23860257 0 29
Remove partial 24046290 84752 30 0
RemoteObj/SlabFrozen 270825 439015 0 0
Total 80014709 80014394

Deactivate Full=23860293(98%) Empty=200(0%) ToHead=0(0%) ToTail=270625(1%)




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