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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=lEU0/0F7eWUHDw+TbGAfXPGAz8GT8RbadBlQcATZx6s/Kjfx0ymCaHoZNLK2kTX0r yaY2jPQASDEFrkih/HPoX0O1+T/+zKolAAcfRwEjB/+/ONoXBTH0Q7xRrfdi22CELZ wgXjTwafR3HYth10+vSB+/YUxr1DC9Fiih6V9cbVC97mhBy80k/udOsCxWMpMWXQqq XSirY2wSDNM5GeUHZTqTcCS7vopZPBiJzSACiuYxYlu3qDADAQpprhmM/eOtWVRI2/ v7TiKUlOp0uKl7iyq/ML6Lz19/DltoIUmfwgUYy8i4lZ7JqYYWW+OuLE6OPlT7Uc+N 006AOdDV5mxeA== Message-ID: Date: Mon, 7 Aug 2023 10:21:05 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Content-Language: en-US To: Jaegeuk Kim References: <65143701-4c19-ab66-1500-abd1162639cd@kernel.org> <330c96f7-fbad-dd17-6368-f1378b3b5375@kernel.org> <87acf602-1587-0615-909d-6e60c66c3cda@kernel.org> <5e5f830b-1b13-4893-fbb0-4c7e99ec9f32@kernel.org> From: Chao Yu In-Reply-To: X-Headers-End: 1qSpru-0007xo-89 Subject: Re: [f2fs-dev] [PATCH v2] f2fs: do not issue small discard commands during checkpoint 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-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On 2023/8/5 4:52, Jaegeuk Kim wrote: > On 07/25, Chao Yu wrote: >> On 2023/7/22 4:23, Jaegeuk Kim wrote: >>> On 07/13, Chao Yu wrote: >>>> On 2023/7/12 23:55, Jaegeuk Kim wrote: >>>>> On 07/12, Chao Yu wrote: >>>>>> On 2023/7/12 0:37, Jaegeuk Kim wrote: >>>>>>> On 07/06, Chao Yu wrote: >>>>>>>> On 2023/7/6 1:30, Jaegeuk Kim wrote: >>>>>>>>> On 07/04, Chao Yu wrote: >>>>>>>>>> On 2023/7/4 18:53, Jaegeuk Kim wrote: >>>>>>>>>>> On 07/03, Chao Yu wrote: >>>>>>>>>>>> On 2023/6/15 0:10, Jaegeuk Kim wrote: >>>>>>>>>>>>> If there're huge # of small discards, this will increase checkpoint latency >>>>>>>>>>>>> insanely. Let's issue small discards only by trim. >>>>>>>>>>>>> >>>>>>>>>>>>> Signed-off-by: Jaegeuk Kim >>>>>>>>>>>>> --- >>>>>>>>>>>>> >>>>>>>>>>>>> Change log from v1: >>>>>>>>>>>>> - move the skip logic to avoid dangling objects >>>>>>>>>>>>> >>>>>>>>>>>>> fs/f2fs/segment.c | 2 +- >>>>>>>>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>>>>>>>>>> >>>>>>>>>>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c >>>>>>>>>>>>> index 8c7af8b4fc47..0457d620011f 100644 >>>>>>>>>>>>> --- a/fs/f2fs/segment.c >>>>>>>>>>>>> +++ b/fs/f2fs/segment.c >>>>>>>>>>>>> @@ -2193,7 +2193,7 @@ void f2fs_clear_prefree_segments(struct f2fs_sb_info *sbi, >>>>>>>>>>>>> len = next_pos - cur_pos; >>>>>>>>>>>>> if (f2fs_sb_has_blkzoned(sbi) || >>>>>>>>>>>>> - (force && len < cpc->trim_minlen)) >>>>>>>>>>>>> + !force || len < cpc->trim_minlen) >>>>>>>>>>>>> goto skip; >>>>>>>>>>>> >>>>>>>>>>>> Sorry for late reply. >>>>>>>>>>>> >>>>>>>>>>>> We have a configuration for such case, what do you think of setting >>>>>>>>>>>> max_small_discards to zero? otherwise, w/ above change, max_small_discards >>>>>>>>>>>> logic may be broken? >>>>>>>>>>>> >>>>>>>>>>>> What: /sys/fs/f2fs//max_small_discards >>>>>>>>>>>> Date: November 2013 >>>>>>>>>>>> Contact: "Jaegeuk Kim" >>>>>>>>>>>> Description: Controls the issue rate of discard commands that consist of small >>>>>>>>>>>> blocks less than 2MB. The candidates to be discarded are cached until >>>>>>>>>>>> checkpoint is triggered, and issued during the checkpoint. >>>>>>>>>>>> By default, it is disabled with 0. >>>>>>>>>>>> >>>>>>>>>>>> Or, if we prefer to disable small_discards by default, what about below change: >>>>>>>>>>> >>>>>>>>>>> I think small_discards is fine, but need to avoid long checkpoint latency only. >>>>>>>>>> >>>>>>>>>> I didn't get you, do you mean we can still issue small discard by >>>>>>>>>> fstrim, so small_discards functionality is fine? >>>>>>>>> >>>>>>>>> You got the point. >>>>>>>> >>>>>>>> Well, actually, what I mean is max_small_discards sysfs entry's functionality >>>>>>>> is broken. Now, the entry can not be used to control number of small discards >>>>>>>> committed by checkpoint. >>>>>>> >>>>>>> Could you descrbie this problem first? >>>>>> >>>>>> Oh, alright, actually, I've described this problem literally, but maybe it's not >>>>>> clear, let me give some examples as below: >>>>>> >>>>>> echo 0 > /sys/fs/f2fs/vdb/max_small_discards >>>>>> xfs_io -f /mnt/f2fs/file -c "pwrite 0 2m" -c "fsync" >>>>>> xfs_io /mnt/f2fs/file -c "fpunch 0 4k" >>>>>> sync >>>>>> cat /proc/fs/f2fs/vdb/discard_plist_info |head -2 >>>>>> >>>>>> echo 100 > /sys/fs/f2fs/vdb/max_small_discards >>>>>> rm /mnt/f2fs/file >>>>>> xfs_io -f /mnt/f2fs/file -c "pwrite 0 2m" -c "fsync" >>>>>> xfs_io /mnt/f2fs/file -c "fpunch 0 4k" >>>>>> sync >>>>>> cat /proc/fs/f2fs/vdb/discard_plist_info |head -2 >>>>>> >>>>>> Before the patch: >>>>>> >>>>>> Discard pend list(Show diacrd_cmd count on each entry, .:not exist): >>>>>> 0 . . . . . . . . >>>>>> >>>>>> Discard pend list(Show diacrd_cmd count on each entry, .:not exist): >>>>>> 0 3 1 . . . . . . >>>>>> >>>>>> After the patch: >>>>>> Discard pend list(Show diacrd_cmd count on each entry, .:not exist): >>>>>> 0 . . . . . . . . >>>>>> >>>>>> Discard pend list(Show diacrd_cmd count on each entry, .:not exist): >>>>>> 0 . . . . . . . . >>>>>> >>>>>> So, now max_small_discards can not be used to control small discard number >>>>>> cached by checkpoint. >>>> >>>> Let me explain more: >>>> >>>> Previously, we have two mechanisms to cache & submit small discards: >>>> >>>> a) set max small discard number in /sys/fs/f2fs/vdb/max_small_discards, and checkpoint >>>> will cache small discard candidates w/ configured maximum number. >>>> >>>> b) call FITRIM ioctl, also, checkpoint in f2fs_trim_fs() will cache small discard >>>> candidates w/ configured discard granularity, but w/o limitation of number. FSTRIM >>>> interface is asynchronized, so it won't submit discard directly. >>>> >>>> Finally, discard thread will submit them in background periodically. >>>> >>>> So what I mean is the mechanism a) is broken, since no matter how we configure the >>>> sysfs entry /sys/fs/f2fs/vdb/max_small_discards, checkpoint will not cache small >>>> discard candidates any more. >>> >>> Ok, it seems what I encountered before was adding this small discard even >>> after issuing it by checkpoint. Thoughts? >> >> Do you mean: in f2fs_clear_prefree_segments(), small discard may overlap >> segment granularity discard? > > I didn't dig enough tho, don't think so. Somehow I got a loop as below which > said the same LBA was issued and added back repeatedly, not seen this short log > unfortunately. > >> >> e.g. >> - f2fs_clear_prefree_segments >> - f2fs_issue_discard(0, 512) --- segment granularity discard >> - f2fs_issue_discard(0, 1) --- small discard >> - f2fs_issue_discard(5, 1) --- small discard >> >> Thanks, [snip] >>> f2fs_discard-25-752 [003] ..... 9744.173111: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c0ca, blklen = 0x1 >>> f2fs_discard-25-752 [004] ..... 9744.175348: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c0ca, blklen = 0x1 I don't see any loop via above log, am I missing something? The traces were printed in below call paths, and it printed the same LBAs as expected? - issue_discard_thread - __issue_discard_cmd - __submit_discard_cmd - trace_f2fs_issue_discard 9744.173111: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c0ca, blklen = 0x1 - __wait_all_discard_cmd - __wait_discard_cmd_range - __remove_discard_cmd - trace_f2fs_remove_discard 9744.175348: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c0ca, blklen = 0x1 Thanks, >>> >>>> >>>> So, it needs to fix max_small_discards sysfs functionality? or just drop the >>>> functionality? >>>> >>>>> >>>>> Since we do not submit small discards anymore during checkpoint. Why not relying >>>>> on the discard thread to issue them? >>>> >>>> Sorry, I'm not sure I get your point, do you mean max_small_discards functionality >>>> is obsoleted, so it recommended to use fstrim to cache & submit small discards? >>>> >>>> Let me know, if I'm missing something or misunderstanding the point. >>>> >>>> Thanks, >>>> >>>>> >>>>>> >>>>>> Thanks, >>>>>> >>>>>>> >>>>>>>> >>>>>>>> I think there is another way to achieve "avoid long checkpoint latency caused >>>>>>>> by committing huge # of small discards", the way is we can set max_small_discards >>>>>>>> to small value or zero, w/ such configuration, it will take checkpoint much less >>>>>>>> time or no time to committing small discard due to below control logic: >>>>>>>> >>>>>>>> f2fs_flush_sit_entries() >>>>>>>> { >>>>>>>> ... >>>>>>>> if (!(cpc->reason & CP_DISCARD)) { >>>>>>>> cpc->trim_start = segno; >>>>>>>> add_discard_addrs(sbi, cpc, false); >>>>>>>> } >>>>>>>> ... >>>>>>>> } >>>>>>>> >>>>>>>> add_discard_addrs() >>>>>>>> { >>>>>>>> ... >>>>>>>> while (force || SM_I(sbi)->dcc_info->nr_discards <= >>>>>>>> SM_I(sbi)->dcc_info->max_discards) { >>>>>>>> >>>>>>>> It will break the loop once nr_discards is larger than max_discards, if >>>>>>>> max_discards is set to zero, checkpoint won't take time to handle small discards. >>>>>>>> >>>>>>>> ... >>>>>>>> if (!de) { >>>>>>>> de = f2fs_kmem_cache_alloc(discard_entry_slab, >>>>>>>> GFP_F2FS_ZERO, true, NULL); >>>>>>>> de->start_blkaddr = START_BLOCK(sbi, cpc->trim_start); >>>>>>>> list_add_tail(&de->list, head); >>>>>>>> } >>>>>>>> ... >>>>>>>> } >>>>>>>> ... >>>>>>>> >>>>>>>> Thanks, >>>>>>>> >>>>>>>>> >>>>>>>>>> >>>>>>>>>> Thanks, >>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> From eb89d9b56e817e3046d7fa17165b12416f09d456 Mon Sep 17 00:00:00 2001 >>>>>>>>>>>> From: Chao Yu >>>>>>>>>>>> Date: Mon, 3 Jul 2023 09:06:53 +0800 >>>>>>>>>>>> Subject: [PATCH] Revert "f2fs: enable small discard by default" >>>>>>>>>>>> >>>>>>>>>>>> This reverts commit d618ebaf0aa83d175658aea5291e0c459d471d39 in order >>>>>>>>>>>> to disable small discard by default, so that if there're huge number of >>>>>>>>>>>> small discards, it will decrease checkpoint's latency obviously. >>>>>>>>>>>> >>>>>>>>>>>> Also, this patch reverts 9ac00e7cef10 ("f2fs: do not issue small discard >>>>>>>>>>>> commands during checkpoint"), due to it breaks small discard feature which >>>>>>>>>>>> may be configured via sysfs entry max_small_discards. >>>>>>>>>>>> >>>>>>>>>>>> Fixes: 9ac00e7cef10 ("f2fs: do not issue small discard commands during checkpoint") >>>>>>>>>>>> Signed-off-by: Chao Yu >>>>>>>>>>>> --- >>>>>>>>>>>> fs/f2fs/segment.c | 4 ++-- >>>>>>>>>>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>>>>>>>>>> >>>>>>>>>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c >>>>>>>>>>>> index 14c822e5c9c9..0a313368f18b 100644 >>>>>>>>>>>> --- a/fs/f2fs/segment.c >>>>>>>>>>>> +++ b/fs/f2fs/segment.c >>>>>>>>>>>> @@ -2193,7 +2193,7 @@ void f2fs_clear_prefree_segments(struct f2fs_sb_info *sbi, >>>>>>>>>>>> len = next_pos - cur_pos; >>>>>>>>>>>> >>>>>>>>>>>> if (f2fs_sb_has_blkzoned(sbi) || >>>>>>>>>>>> - !force || len < cpc->trim_minlen) >>>>>>>>>>>> + (force && len < cpc->trim_minlen)) >>>>>>>>>>>> goto skip; >>>>>>>>>>>> >>>>>>>>>>>> f2fs_issue_discard(sbi, entry->start_blkaddr + cur_pos, >>>>>>>>>>>> @@ -2269,7 +2269,7 @@ static int create_discard_cmd_control(struct f2fs_sb_info *sbi) >>>>>>>>>>>> atomic_set(&dcc->queued_discard, 0); >>>>>>>>>>>> atomic_set(&dcc->discard_cmd_cnt, 0); >>>>>>>>>>>> dcc->nr_discards = 0; >>>>>>>>>>>> - dcc->max_discards = MAIN_SEGS(sbi) << sbi->log_blocks_per_seg; >>>>>>>>>>>> + dcc->max_discards = 0; >>>>>>>>>>>> dcc->max_discard_request = DEF_MAX_DISCARD_REQUEST; >>>>>>>>>>>> dcc->min_discard_issue_time = DEF_MIN_DISCARD_ISSUE_TIME; >>>>>>>>>>>> dcc->mid_discard_issue_time = DEF_MID_DISCARD_ISSUE_TIME; >>>>>>>>>>>> -- >>>>>>>>>>>> 2.40.1 >>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>>> f2fs_issue_discard(sbi, entry->start_blkaddr + cur_pos, _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel