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Wed, 18 Sep 2019 03:27:18 +0000 Received: from DGGEMS407-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id CBBD1E842C024FB08F9E; Wed, 18 Sep 2019 11:27:08 +0800 (CST) Received: from [10.134.22.195] (10.134.22.195) by smtp.huawei.com (10.3.19.207) with Microsoft SMTP Server (TLS) id 14.3.439.0; Wed, 18 Sep 2019 11:27:03 +0800 To: Jaegeuk Kim 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> <20190918031257.GA82722@jaegeuk-macbookpro.roam.corp.google.com> From: Chao Yu Message-ID: Date: Wed, 18 Sep 2019 11:26:33 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190918031257.GA82722@jaegeuk-macbookpro.roam.corp.google.com> Content-Language: en-US X-Originating-IP: [10.134.22.195] X-CFilter-Loop: Reflected X-Headers-End: 1iAQcd-001xKz-Qv 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 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? 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