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Message-ID: <71a0d6ff0701102216l7572bc6j10e3a810eab07b08@mail.gmail.com>
Date: Thu, 11 Jan 2007 09:16:14 +0300
From: "Alexander Shishkin" <alexander.shishckin@gmail.com>
To: Aubrey <aubreylee@gmail.com>
Subject: Re: O_DIRECT question
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, akpm@osdl.org,
       mjt@tls.msk.ru
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On 1/11/07, 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.
>
> uClinux use a memory mapped MTD driver to store rootfs, of course it's
> in the ram,
> So I don't need VFS cache to improve performance. And when order > 3,
> __alloc_page() even doesn't try to shrunk cache and slab, just report
> failure.
>
> So my thought is remove cache, or limit it. But currently there seems
> to be no way in the kernel to do it.  So I want to try to use
> O_DIRECT. But it seems not to be a right way.
One possibility might be to poke the open method in struct
file_operations of your fs like

static int my_open_file(struct inode *inode, struct file *filp)
{
        filp->f_flags |= O_DIRECT;
...
}

which is a nasty thing to do but might give you an idea of what happens next.

Regards,
-- 
I like long walks, especially when they are taken by people who annoy me.
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