Messages in this thread Patch in this message | | | Date | Fri, 21 Jul 2023 13:23:12 -0700 | From | Jaegeuk Kim <> | Subject | Re: [f2fs-dev] [PATCH v2] f2fs: do not issue small discard commands during checkpoint |
| |
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 <jaegeuk@kernel.org> > > > > > > > > > > --- > > > > > > > > > > > > > > > > > > > > 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/<disk>/max_small_discards > > > > > > > > > Date: November 2013 > > > > > > > > > Contact: "Jaegeuk Kim" <jaegeuk.kim@samsung.com> > > > > > > > > > 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?
node=0], cp [data=0, node=0, meta=0], app [read=0 (direct=0, buffered=0), mapped=0], compr(buffered=0, mapped=0)], fs [data=0, (gc_data=0, cdata=0), node=0, meta=0] f2fs_discard-25-752 [003] ..... 9744.173085: f2fs_iostat_latency: dev = (254,51), iotype [peak lat.(ms)/avg lat.(ms)/count], rd_data [0/0/0], rd_node [0/0/0], rd_meta [0/0/0], wr_sync_data [0/0/0], wr_sync_node [0/0/0], wr_sync_meta [0/0/0], wr_async_data [0/0/0], wr_async_node [0/0/0], wr_async_meta [0/0/0] f2fs_discard-25-752 [003] ..... 9744.173089: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c0c6, blklen = 0x1 f2fs_discard-25-752 [003] ..... 9744.173111: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c0ca, blklen = 0x1 f2fs_discard-25-752 [003] ..... 9744.173126: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c116, blklen = 0x1 f2fs_discard-25-752 [003] ..... 9744.173140: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c121, blklen = 0x1 f2fs_discard-25-752 [003] ..... 9744.173154: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c15b, blklen = 0x1 f2fs_discard-25-752 [003] ..... 9744.173169: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c16e, blklen = 0x1 f2fs_discard-25-752 [003] ..... 9744.173183: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c181, blklen = 0x1 f2fs_discard-25-752 [004] ..... 9744.175272: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c0a9, blklen = 0x1 f2fs_discard-25-752 [004] ..... 9744.175345: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c0c6, blklen = 0x1 f2fs_discard-25-752 [004] ..... 9744.175348: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c0ca, blklen = 0x1 f2fs_discard-25-752 [004] ..... 9744.175352: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c116, blklen = 0x1 f2fs_discard-25-752 [004] ..... 9744.175354: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c121, blklen = 0x1 f2fs_discard-25-752 [004] ..... 9744.175360: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c15b, blklen = 0x1 f2fs_discard-25-752 [004] ..... 9744.175362: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c16e, blklen = 0x1 f2fs_discard-25-752 [004] ..... 9744.175367: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c181, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.228775: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c197, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.228950: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c1ad, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.228965: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c1b1, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.228994: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c1b3, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.229006: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c27a, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.229017: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c2a3, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.229028: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c2ab, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.229041: f2fs_issue_discard: dev = (254,51), blkstart = 0x18c304, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.230811: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c197, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.230926: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c1ad, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.230929: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c1b1, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.230932: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c1b3, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.230940: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c27a, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.230945: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c2a3, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.230947: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c2ab, blklen = 0x1 f2fs_discard-25-752 [002] ..... 9744.230952: f2fs_remove_discard: dev = (254,51), blkstart = 0x18c304, blklen = 0x1
> > 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 <chao@kernel.org> > > > > > > > > > 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 <chao@kernel.org> > > > > > > > > > --- > > > > > > > > > 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,
| |