linux-ext4 - Re: [PATCH] ext4: check missed return value ext4_sync

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Message-ID: <20100322005013.GB11560@thunk.org>
Date:	Sun, 21 Mar 2010 20:50:13 -0400
From:	tytso@....edu
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: check missed return value ext4_sync_file

On Fri, Mar 12, 2010 at 11:37:43AM +0300, Dmitry Monakhov wrote:
> The most unpleasant part in ext4_sync_file implementation is that 
> barrier is issued on each fsync() call.  So some bad user may perform:
> while(1) fsync(fd);
> which result in bad system performance. And since barrier request is 
> empty it is hard to detect the reason of troubles.
> Off course we may solve it by introducing some sort of dirty flag
> which is set in write_page, and clear in fsync. But it looks as
> ugly workaround.

We could potentially put the dirty flag in the inode instead, and set
it write_prepare() and writepages() code paths.  I'm not entirely sure
it's worth it, though.

> In respect to previous comments the patch reduced to simple missed
> error check fix.

I've added this to the ext4 patch queue, and I will ignore your
earlier version of the patch.

					- Ted
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