Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757832AbZF2Nq7 (ORCPT ); Mon, 29 Jun 2009 09:46:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752167AbZF2Nqv (ORCPT ); Mon, 29 Jun 2009 09:46:51 -0400 Received: from mx2.redhat.com ([66.187.237.31]:58376 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752003AbZF2Nqv (ORCPT ); Mon, 29 Jun 2009 09:46:51 -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> 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 09:46:48 -0400 In-Reply-To: <20090627182617.GX23611@kernel.dk> (Jens Axboe's message of "Sat, 27 Jun 2009 20:26:17 +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: 2138 Lines: 57 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? 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/