linux-kernel - Re: O_DIRECT question

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Date:	Fri, 12 Jan 2007 11:59:43 +0800
From:	"Roy Huang" <royhuang9@...il.com>
To:	Aubrey <aubreylee@...il.com>
Cc:	"Nick Piggin" <nickpiggin@...oo.com.au>,
	"Andrew Morton" <akpm@...l.org>,
	"Linus Torvalds" <torvalds@...l.org>,
	"Hua Zhong" <hzhong@...il.com>, "Hugh Dickins" <hugh@...itas.com>,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	kenneth.w.chen@...el.com, mjt@....msk.ru,
	"Robin Getz" <rgetz@...ckfin.uclinux.org>
Subject: Re: O_DIRECT question

Limiting total page cache can be considered first. Only if total page
cache overrun limit, check whether the file overrun its per-file
limit. If it is true, release partial page cache and wake up kswapd at
the same time.

On 1/12/07, Aubrey <aubreylee@...il.com> wrote:
> On 1/11/07, Roy Huang <royhuang9@...il.com> wrote:
> > On a embedded systerm, limiting page cache can relieve memory
> > fragmentation. There is a patch against 2.6.19, which limit every
> > opened file page cache and total pagecache. When the limit reach, it
> > will release the page cache overrun the limit.
>
> The patch seems to work for me. But some suggestions in my mind:
>
> 1) Can we limit the total page cache, not the page cache per each file?
>     think about if total memory is 128M, 10% of it is 12.8M, here if
> one application is running, it can use 12.8M vfs cache, then the
> performance will probably not be impacted. However, the current patch
> limit the page cache per each file, which means if only one
> application runs it can only use CONFIG_PAGE_LIMIT pages cache. It may
> be small to the application.
> ------------------snip---------------
> if (mapping->nrpages >= mapping->pages_limit)
>                balance_cache(mapping);
> ------------------snip---------------
>
> 2) A percent number should be better to control the value. Can we add
> a proc interface to make the value tunable?
>
> Thanks,
> -Aubrey
>
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