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Thu, 19 Sep 2019 17:11:17 +0000 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 2F179205F4; Thu, 19 Sep 2019 17:11:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568913068; bh=OEV+1wC+4vm2PATQw5wcqrgeL5kclwql7UgVG17lyXk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=J7/671DBTxT5hVE1qFhFcsitJRK79uYLlmTkJg5qNeD5bjsqsJLtzi/Cr1YeSsrmj 0Hrz3gXz44QJ+wpXgTgneuO+ffl/codZOd3xD3UpmFOcRSK0H/cmmOaimSWVyZ1n4m oTNPkthh32csG/I7ORcqOhm9/NNZKpOgHS8+/qOw= Date: Thu, 19 Sep 2019 10:11:07 -0700 From: Jaegeuk Kim To: Chao Yu Message-ID: <20190919171107.GA19030@jaegeuk-macbookpro.roam.corp.google.com> References: <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> <20190918164754.GA88624@jaegeuk-macbookpro.roam.corp.google.com> <7d7e8e46-0261-ddec-881a-e720ca2badac@huawei.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <7d7e8e46-0261-ddec-881a-e720ca2badac@huawei.com> User-Agent: Mutt/1.8.2 (2017-04-18) X-Headers-End: 1iAzxa-00ASUx-Qm Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: do not select same victim right again X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On 09/19, Chao Yu wrote: > On 2019/9/19 0:47, Jaegeuk Kim wrote: > > 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. > > It won't run into a loop because we keep below condition? The following FGGC will be likely to select this victim again, which doesn't mean "this loop" but "loop of f2fs_gc". > > + if (gc_type == FG_GC && seg_freed) > + sbi->cur_victim_sec = NULL_SEGNO; > > if (sync) > goto stop; > > I meant add below logic in addition: > > + if (gc_type == FG_GC) > + sbi->cur_victim_sec = NULL_SEGNO; > > mutex_unlock(&sbi->gc_mutex); > > Thanks, > > > 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) > >>>>>>>>>>> > >>>>>>>>> . > >>>>>>>>> > >>>>>>> . > >>>>>>> > >>>>> . > >>>>> > >>> . > >>> > > . > > _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel