linux-kernel - Re: O_DIRECT question

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Date:	Thu, 11 Jan 2007 09:16:14 +0300
From:	"Alexander Shishkin" <alexander.shishckin@...il.com>
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, akpm@...l.org, mjt@....msk.ru
Subject: Re: O_DIRECT question

On 1/11/07, 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.
>
> 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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