linux-kernel - Re: O_DIRECT question

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Message-ID: <Pine.LNX.4.64.0701110842480.3594@woody.osdl.org>
Date:	Thu, 11 Jan 2007 08:45:02 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	Roy Huang <royhuang9@...il.com>
cc:	Aubrey <aubreylee@...il.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...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
Subject: Re: O_DIRECT question



On Thu, 11 Jan 2007, Roy Huang 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.

I do think that something like this is probably a good idea, even on 
non-embedded setups. We historically couldn't do this, because mapped 
pages were too damn hard to remove, but that's obviously not much of a 
problem any more.

However, the page-cache limit should NOT be some compile-time constant. It 
should work the same way the "dirty page" limit works, and probably just 
default to "feel free to use 90% of memory for page cache".

		Linus
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