From: Andrea Arcangeli <andrea@suse.de>
To: Jeff Dike <jdike@karaya.com>
Cc: Ryan Cumming <bodnar42@phalynx.dhs.org>, linux-kernel@vger.kernel.org
Subject: Re: Special Kernel Modification
Date: Mon, 5 Nov 2001 17:53:37 +0100 [thread overview]
Message-ID: <20011105175337.D18319@athlon.random> (raw)
In-Reply-To: <E160aCK-0001Fs-00@localhost> <200111050552.AAA06451@ccure.karaya.com>
In-Reply-To: <200111050552.AAA06451@ccure.karaya.com>; from jdike@karaya.com on Mon, Nov 05, 2001 at 12:52:51AM -0500
On Mon, Nov 05, 2001 at 12:52:51AM -0500, Jeff Dike wrote:
> bodnar42@phalynx.dhs.org said:
> > > Mounting it synchronous will disable caching in the VM.
> > Who told
> > you that? Synchronous mounting turns off write buffering. Even with
> > "-o sync" writes will still end up in the page cache, they'll just be
> > commited immediately.
>
> Ummm, how about O_DIRECT instead of O_SYNC (or maybe as well, my googling
> hasn't been clear on whether O_DIRECT bypasses the cache on writes as well)?
O_DIRECT is synchronous but only in terms of data, if you want the
metadata to be synchronous as well you need to open with
O_SYNC|O_DIRECT, and even in such case all the metadata reads will came
from cache.
For example if you only care about being able to reach the data after a
crash (not about the inode info) in a file with all its logical blocks
mapped to physical blcoks (no holes) and then you fsync, later you can
as well avoid O_SYNC and you still don't risk to lose data after a crash
because the block mappings never changes, if you grow/shrink the file
you definitely need O_SYNC to be sure the O_DIRECT data is still there
after a crash instead.
Andrea
next prev parent reply other threads:[~2001-11-05 16:54 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-11-05 0:01 Special Kernel Modification Lonnie Cumberland
2001-11-05 0:19 ` Ryan Cumming
2001-11-05 0:29 ` lonnie
2001-11-05 1:04 ` Jan-Benedict Glaw
2001-11-05 3:04 ` Mike Fedyk
2001-11-06 0:34 ` Jorgen Cederlof
2001-11-06 0:38 ` lonnie
2001-11-05 0:22 ` Alan Cox
2001-11-05 0:39 ` Phil Sorber
2001-11-05 0:38 ` Rik van Riel
2001-11-05 1:04 ` Jeremy Jackson
2001-11-05 1:58 ` Jeff Dike
2001-11-05 2:14 ` Ryan Cumming
2001-11-05 4:02 ` Jeff Dike
2001-11-05 3:13 ` Ryan Cumming
2001-11-05 5:52 ` Jeff Dike
2001-11-05 5:30 ` Ryan Cumming
2001-11-05 14:22 ` Jeff Dike
2001-11-05 16:53 ` Andrea Arcangeli [this message]
2001-11-05 20:18 ` Jeff Dike
2001-11-05 19:05 ` Andrea Arcangeli
2001-11-05 0:37 John Weber
[not found] <E160aCK-0001Fs-00@localhost.suse.lists.linux.kernel>
[not found] ` <200111050552.AAA06451@ccure.karaya.com.suse.lists.linux.kernel>
2001-11-05 6:22 ` Andi Kleen
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