linux-kernel - Re: hackbench regression since 2.6.25-rc

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Date:	Mon, 17 Mar 2008 11:35:40 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: hackbench regression since 2.6.25-rc

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@...-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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