From mboxrd@z Thu Jan 1 00:00:00 1970 From: Minchan Kim Subject: Re: [RFC][PATCH v3] readahead: introduce O_RANDOM for POSIX_FADV_RANDOM Date: Tue, 5 Jan 2010 10:46:09 +0900 Message-ID: <28c262361001041746j1270e2d2i79a932efca861dc5@mail.gmail.com> References: <20091225000717.GA26949@yahoo-inc.com> <87aax18xms.fsf@basil.nowhere.org> <20091230051540.GA16308@localhost> <20091230052402.GB26364@localhost> <873a2s8hmp.fsf@basil.nowhere.org> <20100104045020.GA21021@localhost> <28c262361001032120v284e92b5ub1211f3d1fca6140@mail.gmail.com> <20100104121642.GA12266@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Andi Kleen , Andrew Morton , Quentin Barnes , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , Nick Piggin , Steven Whitehouse , David Howells , Al Viro , Jonathan Corbet , Christoph Hellwig To: Wu Fengguang Return-path: Received: from mail-vw0-f192.google.com ([209.85.212.192]:47192 "EHLO mail-vw0-f192.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751883Ab0AEBqL convert rfc822-to-8bit (ORCPT ); Mon, 4 Jan 2010 20:46:11 -0500 In-Reply-To: <20100104121642.GA12266@localhost> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Mon, Jan 4, 2010 at 9:16 PM, Wu Fengguang w= rote: > Hi Minchan, > > On Mon, Jan 04, 2010 at 01:20:49PM +0800, Minchan Kim wrote: >> > --- linux.orig/mm/readahead.c =C2=A0 2010-01-04 12:39:29.000000000= +0800 >> > +++ linux/mm/readahead.c =C2=A0 =C2=A0 =C2=A0 =C2=A02010-01-04 12:= 39:30.000000000 +0800 >> > @@ -501,6 +501,12 @@ void page_cache_sync_readahead(struct ad >> > =C2=A0 =C2=A0 =C2=A0 =C2=A0if (!ra->ra_pages) >> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0return; >> > >> > + =C2=A0 =C2=A0 =C2=A0 /* be dumb */ >> > + =C2=A0 =C2=A0 =C2=A0 if (filp->f_flags & O_RANDOM) { >> > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 force_page_cach= e_readahead(mapping, filp, offset, req_size); >> > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 return; >> > + =C2=A0 =C2=A0 =C2=A0 } >> > + >> >> Let me have a dumb question. :) >> >> How about testing O_RANDOM in front of ra_pages testing? >> >> My intention is that although we turn off ra, it would be better to = read >> contiguous block all at once than readpage() callback doing I/O >> one page at a time. >> >> Is it break some semantics or happen some problem in ondemand readah= ead? > > Yes it will have some problem with shrink_readahead_size_eio(), which > want to disable readahead and use ->readpage() when ra_pages=3D=3D0. > > Do you have specific use case in mind? The file systems that set > ra_pages=3D0 seems to don't need readahead, too. Never mind. It's just out of curiosity. :) I thought although user disable readahead, we could enhance file I/O with one readpages not multiple readpage if we know the user want to read big contiguous blocks. But I though it break current readahead off semantics. right? Thanks for reply about my dumb question, Wu. :) > > Thanks, > Fengguang > --=20 Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel= " in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html