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From: Andrew Morton <akpm@digeo.com>
To: Manfred Spraul <manfred@colorfullife.com>
Cc: Ed Tomlinson <tomlins@cam.org>, linux-kernel@vger.kernel.org
Subject: Re: [patch 3/4] slab reclaim balancing
Date: Thu, 26 Sep 2002 10:37:08 -0700	[thread overview]
Message-ID: <3D9345C4.74CD73B8@digeo.com> (raw)
In-Reply-To: 3D931608.3040702@colorfullife.com

Manfred Spraul wrote:
> 
> > Slab caches no longer hold onto completely empty pages.  Instead, pages
> > are freed as soon as they have zero objects.  This is possibly a
> > performance hit for slabs which have constructors, but it's doubtful.
> 
> It could be a performance hit for slab with just one object - e.g the
> page sized names cache, used in every syscall that has a path name as a
> parameter.
> 
> Ed, have you benchmarked that there is no noticable slowdown?
> e.g. test the time needed for stat("."). on UP, otherwise the SMP arrays
> would perform the caching.
> 

(What Ed said - we do hang onto one page.  And I _have_ measured
cost in kmem_cache_shrink...)

For those things, the caching should be performed in the page
allocator.  This way, when names_cache requests a cache-hot page,
it may get a page which was very recently a (say) pagetable page,
rather than restricting itself only to pages which used to be
a names_cache page.

CPU caches are per-cpu global.  So the hot pages list should be
per-cpu global also.

Martin Bligh seems to have the patches up and running.  It isn't
very finetuned yet, but initial indications are promising:

Before:
Elapsed: 20.18s User: 192.914s System: 48.292s CPU: 1195.6%

After:
Elapsed: 19.798s User: 191.61s System: 43.322s CPU: 1186.4%

That's for a kernel compile.

And from the profiles, it appears that the benefit is coming
from cache locality, not from the buddylist lock amortisation
which we've also designed into those patches.

I need to stop being slack, and get that code into the pipeline.

  parent reply	other threads:[~2002-09-26 17:31 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2002-09-26 14:13 [patch 3/4] slab reclaim balancing Manfred Spraul
2002-09-26 14:20 ` William Lee Irwin III
2002-09-26 15:24   ` Manfred Spraul
2002-09-26 17:37 ` Andrew Morton [this message]
2002-09-26 18:47   ` Manfred Spraul
2002-09-26 19:49     ` Andrew Morton
2002-09-26 20:49       ` Manfred Spraul
2002-09-26 21:39         ` Andrew Morton
2002-09-27  0:41           ` Ed Tomlinson
2002-09-27 17:24             ` Manfred Spraul
2002-09-27 18:26               ` Andrew Morton
2002-09-27 19:38                 ` Manfred Spraul
2002-09-27 19:52                   ` Andrew Morton
2002-09-27 15:59           ` Manfred Spraul
  -- strict thread matches above, loose matches on Subject: below --
2002-09-26  4:08 Andrew Morton
2002-09-26 11:39 ` Ed Tomlinson
2002-09-26 15:09 ` Ed Tomlinson

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