Date: Wed, 10 Jan 2007 22:06:03 -0800
From: Andrew Morton <akpm@osdl.org>
To: Aubrey <aubreylee@gmail.com>
Cc: "Linus Torvalds" <torvalds@osdl.org>, "Hua Zhong" <hzhong@gmail.com>,
       "Hugh Dickins" <hugh@veritas.com>, linux-kernel@vger.kernel.org,
       hch@infradead.org, kenneth.w.chen@intel.com, mjt@tls.msk.ru
Subject: Re: O_DIRECT question
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On Thu, 11 Jan 2007 13:50:53 +0800
Aubrey <aubreylee@gmail.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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