From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755793Ab1K2OaE (ORCPT ); Tue, 29 Nov 2011 09:30:04 -0500 Received: from cantor2.suse.de ([195.135.220.15]:34782 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755733Ab1K2OaC (ORCPT ); Tue, 29 Nov 2011 09:30:02 -0500 Date: Tue, 29 Nov 2011 15:29:58 +0100 From: Jan Kara To: Wu Fengguang Cc: Andrew Morton , Andi Kleen , Linux Memory Management List , linux-fsdevel@vger.kernel.org, LKML Subject: Re: [PATCH 2/9] readahead: snap readahead request to EOF Message-ID: <20111129142958.GJ5635@quack.suse.cz> References: <20111129130900.628549879@intel.com> <20111129131456.145362960@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111129131456.145362960@intel.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 29-11-11 21:09:02, Wu Fengguang wrote: > If the file size is 20kb and readahead request is [0, 16kb), > it's better to expand the readahead request to [0, 20kb), which will > likely save one followup I/O for [16kb, 20kb). > > If the readahead request already covers EOF, trimm it down to EOF. > Also don't set the PG_readahead mark to avoid an unnecessary future > invocation of the readahead code. > > This special handling looks worthwhile because small to medium sized > files are pretty common. > > Signed-off-by: Wu Fengguang > --- > mm/readahead.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > --- linux-next.orig/mm/readahead.c 2011-11-29 11:28:56.000000000 +0800 > +++ linux-next/mm/readahead.c 2011-11-29 11:29:05.000000000 +0800 > @@ -251,8 +251,16 @@ unsigned long max_sane_readahead(unsigne > unsigned long ra_submit(struct file_ra_state *ra, > struct address_space *mapping, struct file *filp) > { > + pgoff_t eof = ((i_size_read(mapping->host)-1) >> PAGE_CACHE_SHIFT) + 1; > + pgoff_t start = ra->start; > int actual; > > + /* snap to EOF */ > + if (start + ra->size + ra->size / 2 > eof) { > + ra->size = eof - start; > + ra->async_size = 0; > + } > + > actual = __do_page_cache_readahead(mapping, filp, > ra->start, ra->size, ra->async_size); Hmm, wouldn't it be cleaner to do this already in ondemand_readahead()? All other updates of readahead window seem to be there. Also shouldn't we take maximum readahead size into account? Reading 3/2 of max readahead window seems like a relatively big deal for large files... Honza -- Jan Kara SUSE Labs, CR