From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jaegeuk Kim Subject: Re: [PATCH] f2fs: skip checkpoint if having a dirty segment but no prefree at BG_GC -> FG_GC Date: Mon, 27 Feb 2017 10:05:28 -0800 Message-ID: <20170227180528.GA2296@jaegeuk.local> References: <20170224204357.220337-1-guoweichao@huawei.com> <20170224184959.GD39009@jaegeuk.local> <20170225195603.GF51627@jaegeuk.local> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from sog-mx-1.v43.ch3.sourceforge.com ([172.29.43.191] helo=mx.sourceforge.net) by sfs-ml-3.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1ciPg5-00011S-Sz for linux-f2fs-devel@lists.sourceforge.net; Mon, 27 Feb 2017 18:05:41 +0000 Received: from mail.kernel.org ([198.145.29.136]) by sog-mx-1.v43.ch3.sourceforge.com with esmtps (TLSv1:AES256-SHA:256) (Exim 4.76) id 1ciPg1-0005bc-F6 for linux-f2fs-devel@lists.sourceforge.net; Mon, 27 Feb 2017 18:05:41 +0000 Content-Disposition: inline In-Reply-To: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net To: Chao Yu Cc: linux-f2fs-devel@lists.sourceforge.net, guoweichao On 02/27, Chao Yu wrote: > On 2017/2/26 3:56, Jaegeuk Kim wrote: > > On 02/25, guoweichao wrote: > >> Hi Jaegeuk, > >> > >> I regard no enough free sections as a precondition when talking about > >> BG_GC -> FG_GC. I mean that for both case a) and b) I mentioned has no enough > >> free sections implicitly. > >> > >> On 2017/2/25 2:49, Jaegeuk Kim wrote: > >>> Hi Weichao, > >>> > >>> On 02/25, Weichao Guo wrote: > >>>> When turning to FG_GC from BG_GC, we need to write checkpoint in 2 cases: > >>>> * a) BG_GC have made some progress, e.g.: some prefree segments. > >>>> * b) There is no victim and no prefree segment. > >>> > >>> You missed > >>> * c) has_not_enough_free_secs() introduced by > >>> 6e17bfbc75a5cb ("f2fs: fix to overcome inline_data floods") > >> As we have enabled SSR for warm node(5b6c6be2d8 ("f2fs: use SSR for warm node as well")), > >> I think inline data floods should not be a problem in most cases. > >>> > >>> And, Yunlong pointed that we can't find a case to avoid write_checkpoint() > >>> mostly due to c) condition. > >> As inline data floods is an extreme case, and there is little possibility caused panic > >> for inline data floods now, there should be lots of chance to skip checkpoint. I mean > >> that we can make some accurate inline data floods checking before writing checkpoint. > > > > For now, the safest way is our first option. So, I decided to start with doing > > checkpoint due to previous inline_data flooding issue even though it's an > > extreme case under SSR. > > > > Anyway, I agree that we need to find a way to detect when to avoid checkpoint. > > Hi all, > > I proposed a approach before, can you please check that one? > > https://www.mail-archive.com/linux-f2fs-devel@lists.sourceforge.net/msg03632.html Oh, right, let's take a look at this. ;) Thanks, > > Thanks, > > > > > Thanks, > > > >>> > >>> Thanks, > >>> > >>>> > >>>> For case a), previously, we also check if there is a dirty segment for > >>>> infering blocks moving in last BG_GC. But dirty segments do not always > >>>> indicate that, BG_GC may just start and do not move any blocks at all. > >>>> Futhermore, skipping checkpoint if there are some dirty segments but no > >>>> prefree segments is OK. > >>> > >>> > >>>> > >>>> Signed-off-by: Weichao Guo > >>>> --- > >>>> fs/f2fs/gc.c | 7 ++++++- > >>>> 1 file changed, 6 insertions(+), 1 deletion(-) > >>>> > >>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c > >>>> index 6c996e3..30d206a 100644 > >>>> --- a/fs/f2fs/gc.c > >>>> +++ b/fs/f2fs/gc.c > >>>> @@ -958,7 +958,12 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync, bool background) > >>>> * enough free sections, we should flush dent/node blocks and do > >>>> * garbage collections. > >>>> */ > >>>> - ret = write_checkpoint(sbi, &cpc); > >>>> + if (prefree_segments(sbi)) > >>>> + ret = write_checkpoint(sbi, &cpc); > >>>> + else if (!__get_victim(sbi, &segno, gc_type) { > >>>> + segno = NULL_SEGNO; > >>>> + ret = write_checkpoint(sbi, &cpc); > >>>> + } > >>>> if (ret) > >>>> goto stop; > >>>> } else if (gc_type == BG_GC && !background) { > >>>> -- > >>>> 2.10.1 > >>> > >>> . > >>> > >> > >> Thanks, > >> Weichao > > > > . > > ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot