From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jamie Lokier Subject: Re: [rfc][patch] mm: direct io less aggressive syncs and invalidates Date: Wed, 29 Oct 2008 00:56:00 +0000 Message-ID: <20081029005600.GA24030@shareable.org> References: <20081028155421.GC3082@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 mail2.shareable.org ([80.68.89.115]:55203 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753480AbYJ2A4D (ORCPT ); Tue, 28 Oct 2008 20:56:03 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Jeff Moyer wrote: > > 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? It seems that could be easily tested in one of the test suites, by writing a page without O_DIRECT to make a dirty page, then reading the same page with O_DIRECT. Do it a few times to be sure. Do the test suites verify O_DIRECT / page-cache coherency? Cheers, -- Jamie