From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8FD82C4CECD for ; Wed, 18 Sep 2019 03:13:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5BC562189D for ; Wed, 18 Sep 2019 03:13:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568776381; bh=2nL15fdb42znZn7Z0uLezA9HuQwulYK2zVQeGOjDF7o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=Lg1uO/9AlKoLtxGs+VVs2KSLraRTJrRk3WcTRj5TyvXmRoAkNCXgWsVpCX9IXSRu9 PLbW87rf8nzdFyLJac9a8jaVG0bXYIqAL9laj+q53owTEiMR3p08c6STJfZM4eoqS8 LNHjTzL4Q2Ub2n50Lhj04AlEJyvTeOyUUYkXzaA0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728158AbfIRDNA (ORCPT ); Tue, 17 Sep 2019 23:13:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:51624 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726786AbfIRDNA (ORCPT ); Tue, 17 Sep 2019 23:13:00 -0400 Received: from localhost (unknown [104.132.0.81]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9985F21855; Wed, 18 Sep 2019 03:12:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568776378; bh=2nL15fdb42znZn7Z0uLezA9HuQwulYK2zVQeGOjDF7o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=crVCuysuqQ+TWaYTS224Ytoemrl6mkiBBkbsaqjqxs/PqOviAmadvOAW4qV8lKsR5 pAU1m5zqurS9rw5WJwzUdu98mLAnz5y4Y7zD3OSSrwDH3aAyuyYLKi/GYmvajftRT2 Eq89aVkVQgCc4sBHgE9zaWHcqSXWUTl3gaXMjQRc= Date: Tue, 17 Sep 2019 20:12:57 -0700 From: Jaegeuk Kim To: Chao Yu Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: do not select same victim right again Message-ID: <20190918031257.GA82722@jaegeuk-macbookpro.roam.corp.google.com> References: <20190909012532.20454-1-jaegeuk@kernel.org> <69933b7f-48cc-47f9-ba6f-b5ca8f733cba@huawei.com> <20190909080654.GD21625@jaegeuk-macbookpro.roam.corp.google.com> <97237da2-897a-8420-94de-812e94aa751f@huawei.com> <20190909120443.GA31108@jaegeuk-macbookpro.roam.corp.google.com> <27725e65-53fe-5731-0201-9959b8ef6b49@huawei.com> <20190916153736.GA2493@jaegeuk-macbookpro.roam.corp.google.com> <20190917205501.GA60683@jaegeuk-macbookpro.roam.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.8.2 (2017-04-18) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/18, Chao Yu wrote: > On 2019/9/18 4:55, Jaegeuk Kim wrote: > > On 09/17, Chao Yu wrote: > >> On 2019/9/16 23:37, Jaegeuk Kim wrote: > >>> On 09/16, Chao Yu wrote: > >>>> On 2019/9/9 20:04, Jaegeuk Kim wrote: > >>>>> On 09/09, Chao Yu wrote: > >>>>>> On 2019/9/9 16:06, Jaegeuk Kim wrote: > >>>>>>> On 09/09, Chao Yu wrote: > >>>>>>>> On 2019/9/9 9:25, Jaegeuk Kim wrote: > >>>>>>>>> GC must avoid select the same victim again. > >>>>>>>> > >>>>>>>> Blocks in previous victim will occupy addition free segment, I doubt after this > >>>>>>>> change, FGGC may encounter out-of-free space issue more frequently. > >>>>>>> > >>>>>>> Hmm, actually this change seems wrong by sec_usage_check(). > >>>>>>> We may be able to avoid this only in the suspicious loop? > >>>>>>> > >>>>>>> --- > >>>>>>> fs/f2fs/gc.c | 2 +- > >>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-) > >>>>>>> > >>>>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c > >>>>>>> index e88f98ddf396..5877bd729689 100644 > >>>>>>> --- a/fs/f2fs/gc.c > >>>>>>> +++ b/fs/f2fs/gc.c > >>>>>>> @@ -1326,7 +1326,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync, > >>>>>>> round++; > >>>>>>> } > >>>>>>> > >>>>>>> - if (gc_type == FG_GC) > >>>>>>> + if (gc_type == FG_GC && seg_freed) > >>>>>> > >>>>>> That's original solution Sahitya provided to avoid infinite loop of GC, but I > >>>>>> suggest to find the root cause first, then we added .invalid_segmap for that > >>>>>> purpose. > >>>>> > >>>>> I've checked the Sahitya's patch. So, it seems the problem can happen due to > >>>>> is_alive or atomic_file. > >>>> > >>>> For some conditions, this doesn't help, for example, two sections contain the > >>>> same fewest valid blocks, it will cause to loop selecting them if it fails to > >>>> migrate blocks. > >>>> > >>>> How about keeping it as it is to find potential bug. > >>> > >>> I think it'd be fine to merge this. Could you check the above scenario in more > >>> detail? > >> > >> I haven't saw this in real scenario yet. > >> > >> What I mean is if there is a bug (maybe in is_alive()) failing us to GC on one > >> section, when that bug happens in two candidates, there could be the same > >> condition that GC will run into loop (select A, fail to migrate; select B, fail > >> to migrate, select A...). > >> > >> But I guess the benefit of this change is, if FGGC fails to migrate block due to > >> i_gc_rwsem race, selecting another section and later retrying previous one may > >> avoid lock race, right? > > > > In any case, I think this can avoid potenial GC loop. At least to me, it'd be > > quite risky, if we remain this just for debugging purpose only. > > Yup, > > One more concern is would this cur_victim_sec remain after FGGC? then BGGC/SSR > will always skip the section cur_victim_sec points to. Then, we can get another loop before using it by BGGC/SSR. > > So could we reset cur_victim_sec in the end of FGGC? > > Thanks, > > > > >> > >> Thanks, > >> > >>> > >>> Thanks, > >>> > >>>> > >>>> Thanks, > >>>> > >>>>> > >>>>>> > >>>>>> Thanks, > >>>>>> > >>>>>>> sbi->cur_victim_sec = NULL_SEGNO; > >>>>>>> > >>>>>>> if (sync) > >>>>>>> > >>>>> . > >>>>> > >>> . > >>> > > . > >