linux-kernel - Re: O_DIRECT question

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Message-Id: <20070110220603.f3685385.akpm@osdl.org>
Date:	Wed, 10 Jan 2007 22:06:03 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Aubrey <aubreylee@...il.com>
Cc:	"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
Subject: Re: O_DIRECT question

On Thu, 11 Jan 2007 13:50:53 +0800
Aubrey <aubreylee@...il.com> wrote:

> Firstly I want to say I'm working on no-mmu arch and uClinux.
> After much of file operations VFS cache eat up all of the memory.
> At this time, if an application request memory which order > 3, the
> kernel will report failure.

nommu kernels should probably run reclaim for higher-order allocations as
well.

That's rather a blunt instrument.  The "lumpy reclaim" patches in -mm
provide a much better approach, but they need more work yet (although I
don't immediately recall what's needed).

In the interim you could do the old "echo 3 > /proc/sys/vm/drop_caches"
thing, but that's terribly crude - drop_caches is really only for debugging
and benchmarking.
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