From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Chinner Subject: Re: [rfc][patch] mm: direct io less aggressive syncs and invalidates Date: Thu, 30 Oct 2008 08:47:50 +1100 Message-ID: <20081029214750.GJ17077@disturbed> References: <20081028155421.GC3082@wotan.suse.de> <20081028235221.GB15599@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Nick Piggin , Andrew Morton , linux-fsdevel@vger.kernel.org, mpatocka@redhat.com To: Jeff Moyer Return-path: Received: from ipmail04.adl2.internode.on.net ([203.16.214.57]:26030 "EHLO ipmail04.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753681AbYJ2Vry (ORCPT ); Wed, 29 Oct 2008 17:47:54 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, Oct 29, 2008 at 09:12:24AM -0400, Jeff Moyer wrote: > 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 XFS does it's own flush and invalidate before calling into the generic direct I/O code, so the above patch is safe from an XFS perspective. Cheers, Dave. -- Dave Chinner david@fromorbit.com