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 ECC5AC4CEC4 for ; Wed, 18 Sep 2019 16:47:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BD3A921907 for ; Wed, 18 Sep 2019 16:47:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568825277; bh=dT8WG2DycZhc/fpKSgROJHbA/O6sl74Vzx7O0UdeWt8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=iCLuRcrP6I09U4Tz0jx03i0ejvdq6fUsarXKCyhrD9RtudLpkWSAL8j/DY+LIn9kz oCxwizzK7sL8MGjD8Cu4J2lkbjmaB92PTbJ/DV7wfWKynbEnPLgtVSaGQPtNoronbu ITYwS5nDEwgHMFVvUttsft1RkazqV7aMpVa7tQuw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387750AbfIRQr5 (ORCPT ); Wed, 18 Sep 2019 12:47:57 -0400 Received: from mail.kernel.org ([198.145.29.99]:51026 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387733AbfIRQr4 (ORCPT ); Wed, 18 Sep 2019 12:47:56 -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 52D82218AE; Wed, 18 Sep 2019 16:47:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568825275; bh=dT8WG2DycZhc/fpKSgROJHbA/O6sl74Vzx7O0UdeWt8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=saox0hpaKbeFfsuq0ImpXJzHzGWB4nd3hnPuSOYOCOgdZvdNG67r4gVp1K7nk0Ogp gCnuFmZMH+SrPbsOytnPBQ2F3vU9O15kAaR0wcIOaIYjOuuCOvexB738PHrFl28MOC 4qE+8aQwLwNjSBW39jdMgWCRlMRwmDZq9ctPBaGw= Date: Wed, 18 Sep 2019 09:47:54 -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: <20190918164754.GA88624@jaegeuk-macbookpro.roam.corp.google.com> References: <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> <20190918031257.GA82722@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 11:12, Jaegeuk Kim wrote: > > 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. > > I guess I didn't catch your point, do you mean, if we reset it in the end of > FGGC, we may encounter the loop during BGGC/SSR? FGGC failed in a loop and last victim was remained in cur_victim_sec. Next FGGC kicked in and did the same thing again. I don't expect BGGC/SSR wants to select this victim much, since it will have CB policy. > > I meant: > > f2fs_gc() > ... > > + if (gc_type == FG_GC) > + sbi->cur_victim_sec = NULL_SEGNO; > > mutex_unlock(&sbi->gc_mutex); > > put_gc_inode(&gc_list); > ... > > Thanks, > > > > >> > >> 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) > >>>>>>>>> > >>>>>>> . > >>>>>>> > >>>>> . > >>>>> > >>> . > >>> > > . > >