Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756501AbZF2Rot (ORCPT ); Mon, 29 Jun 2009 13:44:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753195AbZF2Rom (ORCPT ); Mon, 29 Jun 2009 13:44:42 -0400 Received: from mx2.redhat.com ([66.187.237.31]:48674 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752303AbZF2Rol (ORCPT ); Mon, 29 Jun 2009 13:44:41 -0400 From: Jeff Moyer To: Jens Axboe Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org Subject: Re: [PATCH 2/2] cfq-iosched: get rid of the need for __GFP_FAIL in cfq_find_alloc_queue() References: <1246007120-24034-1-git-send-email-jens.axboe@oracle.com> <1246007120-24034-3-git-send-email-jens.axboe@oracle.com> <20090627182617.GX23611@kernel.dk> <20090629173418.GN23611@kernel.dk> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Date: Mon, 29 Jun 2009 13:44:07 -0400 In-Reply-To: <20090629173418.GN23611@kernel.dk> (Jens Axboe's message of "Mon, 29 Jun 2009 19:34:18 +0200") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.60 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2507 Lines: 66 Jens Axboe writes: > On Mon, Jun 29 2009, Jeff Moyer wrote: >> Jens Axboe writes: >> >> > On Fri, Jun 26 2009, Jeff Moyer wrote: >> >> Jens Axboe writes: >> >> >> >> > Setup an emergency fallback cfqq that we allocate at IO scheduler init >> >> > time. If the slab allocation fails in cfq_find_alloc_queue(), we'll just >> >> > punt IO to that cfqq instead. This ensures that cfq_find_alloc_queue() >> >> > never fails without having to ensure free memory. >> >> > >> >> > Signed-off-by: Jens Axboe >> >> > --- >> >> > block/cfq-iosched.c | 124 +++++++++++++++++++++++++++----------------------- >> >> > 1 files changed, 67 insertions(+), 57 deletions(-) >> >> > >> >> > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c >> >> > index c760ae7..91e7e0b 100644 >> >> > --- a/block/cfq-iosched.c >> >> > +++ b/block/cfq-iosched.c >> >> > + /* >> >> > + * Fallback dummy cfqq for extreme OOM conditions >> >> > + */ >> >> > + struct cfq_queue oom_cfqq; >> >> >> >> OK, so you're embedding a cfqq into the cfqd. That's 136 bytes, so I >> >> guess that's not too bad. >> >> >> >> > + /* >> >> > + * Our fallback cfqq if cfq_find_alloc_queue() runs into OOM issues. >> >> > + * Grab a permanent reference to it, so that the normal code flow >> >> > + * will not attempt to free it. >> >> > + */ >> >> > + cfq_init_cfqq(cfqd, &cfqd->oom_cfqq, 1, 0); >> >> > + atomic_inc(&cfqd->oom_cfqq.ref); >> >> > + >> >> >> >> I guess this is so we never try to free it, good. ;) >> >> >> >> One issue I have with this patch is that, if a task happens to run into >> >> this condition, there is no way out. It will always have the oom_cfqq >> >> as it's cfqq. Can't we fix that if we recover from the OOM condition? >> > >> > Yeah, I fixed that about an hour after posting the patches. See: >> > >> > http://git.kernel.dk/?p=linux-2.6-block.git;a=commit;h=0370bc158cb1d5faa4b8a38c0de3211f0fd5bd64 >> > >> > I didn't post the 3/2 patch though. >> >> OK, that looks better. Are you reposting the series, then? > > Yeah, I'll fold the last two patches together and repost. When you do, you can add my: Reviewed-by: Jeff Moyer Cheers, Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/