From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Moyer Subject: Re: [rfc][patch] mm: direct io less aggressive syncs and invalidates Date: Wed, 29 Oct 2008 09:12:24 -0400 Message-ID: References: <20081028155421.GC3082@wotan.suse.de> <20081028235221.GB15599@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andrew Morton , linux-fsdevel@vger.kernel.org, mpatocka@redhat.com To: Nick Piggin Return-path: Received: from mx2.redhat.com ([66.187.237.31]:57289 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753451AbYJ2NM6 (ORCPT ); Wed, 29 Oct 2008 09:12:58 -0400 In-Reply-To: <20081028235221.GB15599@wotan.suse.de> (Nick Piggin's message of "Wed, 29 Oct 2008 00:52:21 +0100") Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Nick Piggin writes: > On Tue, Oct 28, 2008 at 05:11:02PM -0400, Jeff Moyer wrote: >> Nick Piggin writes: >> > Index: linux-2.6/mm/filemap.c >> > =================================================================== >> > --- linux-2.6.orig/mm/filemap.c 2008-10-03 11:21:31.000000000 +1000 >> > +++ linux-2.6/mm/filemap.c 2008-10-03 12:00:17.000000000 +1000 >> > @@ -1304,11 +1304,8 @@ generic_file_aio_read(struct kiocb *iocb >> > goto out; /* skip atime */ >> > size = i_size_read(inode); >> > if (pos < size) { >> > - retval = filemap_write_and_wait(mapping); >> > - if (!retval) { >> > - retval = mapping->a_ops->direct_IO(READ, iocb, >> > + retval = mapping->a_ops->direct_IO(READ, iocb, >> > iov, pos, nr_segs); >> > - } >> >> So why is it safe to get rid of this? Can't this result in reading >> stale data from disk? > > AFAIKS, __blockdev_direct_IO is doing the same thing for us, when it > encounters a READ. I should have documented this change. This is one > thing I'm not *quite* sure of there might be a path do the block device > that I haven't considered, and which does not do the sync... Well, that's if dio_lock_type != DIO_NO_LOCKING. cscope shows the following callers of blockdev_direct_IO_no_locking: gfs2_direct_IO ocfs2_direct_IO xfs_vm_direct_IO and of course blkdev_direct_IO I can't say whether all of these callers are safe. They certainly don't appear to be safe to me. Cheers, Jeff