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Re: [PATCH 3/3] filemap: don't call generic_write_sync for -EIOCBQUEUED

To: Jeff Moyer <jmoyer@xxxxxxxxxx>
Subject: Re: [PATCH 3/3] filemap: don't call generic_write_sync for -EIOCBQUEUED
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Mon, 6 Feb 2012 14:55:47 -0500
Cc: Jan Kara <jack@xxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <x497gzzrkfa.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
References: <1327698949-12616-1-git-send-email-jmoyer@xxxxxxxxxx> <1327698949-12616-4-git-send-email-jmoyer@xxxxxxxxxx> <20120202175219.GB6640@xxxxxxxxxxxxx> <x497gzzrkfa.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Feb 06, 2012 at 11:33:29AM -0500, Jeff Moyer wrote:
> > code, right? Before that we'd drain the IO queue when cache flush is issued
> > and thus effectively wait for IO completion...
> 
> Right, though hch seems to think even then the problem existed.

I was wrong, using -o barrier it didn't.  That was however not something
people using O_SYNC heavy production loads would do, they'd use disabled
caches and nobarrier.

> > Also I was thinking whether we couldn't implement the fix in VFS. Basically
> > it would be the same like the fix for ext4. Like having a per-sb workqueue
> > and queue work calling generic_write_sync() from end_io handler when the
> > file is O_SYNC? That would solve the issue for all filesystems...
> 
> Well, that would require buy-in from the other file system developers.
> What do the XFS folks think?

I don't think using that code for XFS makes sene.  But just like
generic_write_sync there's no reason it can't be added to generic code,
just make sure only generic_file_aio_write/__generic_file_aio_write use
it, but generic_file_buffered_write and generic_file_direct_write stay
clear of it.

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