linux-kernel - Re: mmap vs fs cache

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Message-ID: <513A02FC.4070208@genband.com>
Date:	Fri, 08 Mar 2013 09:25:48 -0600
From:	Chris Friesen <chris.friesen@...band.com>
To:	Howard Chu <hyc@...as.com>
CC:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
	linux-kernel <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: mmap vs fs cache

On 03/08/2013 09:00 AM, Howard Chu wrote:

> First obvious conclusion - kswapd is being too aggressive. When free
> memory hits the low watermark, the reclaim shrinks slapd down from 25GB
> to 18-19GB, while the page cache still contains ~7GB of unmapped pages.
> Ideally I'd like a tuning knob so I can say to keep no more than 2GB of
> unmapped pages in the cache. (And the desired effect of that would be to
> allow user processes to grow to 30GB total, in this case.)
>
> I mentioned this "unmapped page cache control" post already
> http://lwn.net/Articles/436010/ but it seems that the idea was
> ultimately rejected. Is there anything else similar in current kernels?

Sorry, I'm not aware of anything.  I'm not a filesystem/vm guy though, 
so maybe there's something I don't know about.

I would have expected both posix_madvise(..POSIX_MADV_RANDOM) and 
swappiness to help, but it doesn't sound like they're working.

Chris
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