linux-ext4 - Re: per inode fsync optimization question

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Message-ID: <20130403145055.GD14667@quack.suse.cz>
Date:	Wed, 3 Apr 2013 16:50:55 +0200
From:	Jan Kara <jack@...e.cz>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	ext4 development <linux-ext4@...r.kernel.org>,
	Jan Kara <jack@...e.cz>
Subject: Re: per inode fsync optimization question

On Wed 03-04-13 18:21:46, Dmitry Monakhov wrote:
> inode store i_sync_tid and i_datasync_tid  in order to optimize journal
> flushes and wait for commits only when necessary, but
> fields are declared as tid_t(not atomic_t as it done in ext3) so we
> have not synchronization between readers and writers, so gcc and cpu
> is allowed to perform prefetch, cache and other stuff.
> Looks like a bug, right?
  Reads and writes to atomic_t aren't guaranteed to be any kind of a
barrier (if fact they are compiled as simple stores and loads on x86). Only
arithmetic operations on atomic types are special. So using tid_t is just
fine.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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