linux-kernel - Re: PERF: performance tests with the split LRU VM in -mm

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Date:	Mon, 28 Jul 2008 19:57:13 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: PERF: performance tests with the split LRU VM in -mm

On Mon, 28 Jul 2008 16:41:24 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> > Andrew, what is your preference between:
> > 	http://lkml.org/lkml/2008/7/15/465
> > and
> > 	http://marc.info/?l=linux-mm&m=121683855132630&w=2
> > 
> 
> Boy.  They both seem rather hacky special-cases.  But that doesn't mean
> that they're undesirable hacky special-cases.  I guess the second one
> looks a bit more "algorithmic" and a bit less hacky-special-case.  But
> it all depends on testing..

I prefer the second one, since it removes the + 1 magic (at least,
for the higher priorities), instead of adding new magic like the
other patch does.

> On a different topic, these:
> 
> vmscan-give-referenced-active-and-unmapped-pages-a-second-trip-around-the-lru.patch
> vm-dont-run-touch_buffer-during-buffercache-lookups.patch
> 
> have been floating about in -mm for ages, awaiting demonstration that
> they're a net benefit.  But all of this new page-reclaim rework was
> built on top of those two patches and incorporates and retains them.
> 
> I could toss them out, but that would require some rework and would
> partially invalidate previous testing and who knows, they _might_ be
> good patches.  Or they might not be.
> 
> What are your thoughts?

I believe you should definately keep those.  Being able to better
preserve actively accessed file pages could be a good benefit and
we have yet to discover a downside to those patches.

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