From: Hugh Dickins <hugh@veritas.com>
To: Yingchao Zhou <yc_zhou@ncic.ac.cn>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [RFC]should swap-file opened with O_DIRECT?
Date: Mon, 10 Oct 2005 16:06:06 +0100 (BST) [thread overview]
Message-ID: <Pine.LNX.4.61.0510101558140.1168@goblin.wat.veritas.com> (raw)
In-Reply-To: <20051010135229.D29B5FB048@gatekeeper.ncic.ac.cn>
On Mon, 10 Oct 2005, Yingchao Zhou wrote:
>
> The sys_swapon system call open the swap-file through
> filp_open(..., O_RDWR|O_LARGEFILE,...).
> In this way, I think that the pageout process of anonymous
> pages finally will write them out through (swap-file)->f_ops->write,
No, they are written out by swap_writepage. The opening in sys_swapon
gets a handle of what is to be used for swap, but it then goes its own way.
> and it will result in caches of swapfile. However, swapping only
> happens when memory is tight. So why not set O_DIRECT? Is there any
> special reason to keep caches of swapfile?
Caches of swapfile are useful (but yes, can be discarded when memory
is tight). There's nothing indirect about them: the page that is mapped
into userspace gets written to disk, the page that is read in from disk
gets mapped back into userspace.
Hugh
prev parent reply other threads:[~2005-10-10 15:06 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-10-10 13:46 Yingchao Zhou
2005-10-10 15:06 ` Hugh Dickins [this message]
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