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Date: Wed, 22 Feb 2017 20:25:57 -0800
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <yuchao0@...wei.com>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 3/6] f2fs: remove batched discard in
f2fs_trim_fs
On 02/23, Chao Yu wrote:
> On 2017/2/23 5:55, Jaegeuk Kim wrote:
> > On 02/22, Chao Yu wrote:
> >> On 2017/1/13 6:44, Jaegeuk Kim wrote:
> >>> We don't need to do multiple checkpoints, since we don't actually wait for
> >>> completion of discard commands during checkpoint.
> >>> Instead, we still need to avoid very big discard commands, since that large
> >>> discard can interfere block allocation.
> >>
> >> I hope we can keep this functionality and related sysfs interface, the main
> >> concern is that: for 16T size fragmented partition, at most there will be
> >> ~sizeof(u32)/2 4K blocks which could be invalid and needed to be discarded.
> >> After removal of in-batch discard, we have to handle billions of discard message
> >> with gc_mutex & cp_rwsem held, which will freeze f2fs for very long time.
> >
> > The baseline of this patch is that we have a kernel thread to issue discard
> > commands asynchronously. So, I don't expect such the huge latency anymore.
>
> Yes, I know async kernel thread was already introduced, and we can expect such
> implementation can help to reduce huge handling latency. But still in checkpoint
> we need to check region of invalid block and send the pending discard entries to
> kernel thread, so what I concern is that in scenario of there is huge number of
> discard messages, we will still face long latency with cp lock held.
Okay, I removed the below patch now, and changed 4GB range by default. ;)
Thanks,
>
> Thanks,
>
> >
> > Thanks,
> >
> >>
> >> So I suggest we just set trim_sections to 512 segments (covers one GB) by
> >> default. How do you think?
> >>
> >> Thanks,
> >>
> >>>
> >>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> >>> ---
> >>> Documentation/ABI/testing/sysfs-fs-f2fs | 6 ------
> >>> fs/f2fs/f2fs.h | 9 +-------
> >>> fs/f2fs/segment.c | 38 +++++++++++----------------------
> >>> fs/f2fs/super.c | 2 --
> >>> 4 files changed, 14 insertions(+), 41 deletions(-)
> >>>
> >>> diff --git a/Documentation/ABI/testing/sysfs-fs-f2fs b/Documentation/ABI/testing/sysfs-fs-f2fs
> >>> index a809f6005f14..df6b3f6e164a 100644
> >>> --- a/Documentation/ABI/testing/sysfs-fs-f2fs
> >>> +++ b/Documentation/ABI/testing/sysfs-fs-f2fs
> >>> @@ -75,12 +75,6 @@ Contact: "Jaegeuk Kim" <jaegeuk.kim@...sung.com>
> >>> Description:
> >>> Controls the memory footprint used by f2fs.
> >>>
> >>> -What: /sys/fs/f2fs/<disk>/trim_sections
> >>> -Date: February 2015
> >>> -Contact: "Jaegeuk Kim" <jaegeuk@...nel.org>
> >>> -Description:
> >>> - Controls the trimming rate in batch mode.
> >>> -
> >>> What: /sys/fs/f2fs/<disk>/cp_interval
> >>> Date: October 2015
> >>> Contact: "Jaegeuk Kim" <jaegeuk@...nel.org>
> >>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >>> index 548e75d18ec1..a2850bf2a487 100644
> >>> --- a/fs/f2fs/f2fs.h
> >>> +++ b/fs/f2fs/f2fs.h
> >>> @@ -128,11 +128,7 @@ enum {
> >>> CP_DISCARD,
> >>> };
> >>>
> >>> -#define DEF_BATCHED_TRIM_SECTIONS 2
> >>> -#define BATCHED_TRIM_SEGMENTS(sbi) \
> >>> - (SM_I(sbi)->trim_sections * (sbi)->segs_per_sec)
> >>> -#define BATCHED_TRIM_BLOCKS(sbi) \
> >>> - (BATCHED_TRIM_SEGMENTS(sbi) << (sbi)->log_blocks_per_seg)
> >>> +#define MAX_DISCARD_BLOCKS(sbi) (1 << (sbi)->log_blocks_per_seg)
> >>> #define DEF_CP_INTERVAL 60 /* 60 secs */
> >>> #define DEF_IDLE_INTERVAL 5 /* 5 secs */
> >>>
> >>> @@ -638,9 +634,6 @@ struct f2fs_sm_info {
> >>> int nr_discards; /* # of discards in the list */
> >>> int max_discards; /* max. discards to be issued */
> >>>
> >>> - /* for batched trimming */
> >>> - unsigned int trim_sections; /* # of sections to trim */
> >>> -
> >>> struct list_head sit_entry_set; /* sit entry set list */
> >>>
> >>> unsigned int ipu_policy; /* in-place-update policy */
> >>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>> index 73282108fa33..e6f3c6db7616 100644
> >>> --- a/fs/f2fs/segment.c
> >>> +++ b/fs/f2fs/segment.c
> >>> @@ -823,7 +823,8 @@ static void __add_discard_entry(struct f2fs_sb_info *sbi,
> >>> if (!list_empty(head)) {
> >>> last = list_last_entry(head, struct discard_entry, list);
> >>> if (START_BLOCK(sbi, cpc->trim_start) + start ==
> >>> - last->blkaddr + last->len) {
> >>> + last->blkaddr + last->len &&
> >>> + last->len <= MAX_DISCARD_BLOCKS(sbi)) {
> >>> last->len += end - start;
> >>> goto done;
> >>> }
> >>> @@ -1513,36 +1514,25 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
> >>> "Found FS corruption, run fsck to fix.");
> >>> goto out;
> >>> }
> >>> + if (sbi->discard_blks == 0)
> >>> + goto out;
> >>>
> >>> /* start/end segment number in main_area */
> >>> start_segno = (start <= MAIN_BLKADDR(sbi)) ? 0 : GET_SEGNO(sbi, start);
> >>> end_segno = (end >= MAX_BLKADDR(sbi)) ? MAIN_SEGS(sbi) - 1 :
> >>> GET_SEGNO(sbi, end);
> >>> + /*
> >>> + * do checkpoint to issue discard commands safely since we now can
> >>> + * use async discard.
> >>> + */
> >>> cpc.reason = CP_DISCARD;
> >>> cpc.trim_minlen = max_t(__u64, 1, F2FS_BYTES_TO_BLK(range->minlen));
> >>> + cpc.trim_start = start_segno;
> >>> + cpc.trim_end = end_segno;
> >>>
> >>> - /* do checkpoint to issue discard commands safely */
> >>> - for (; start_segno <= end_segno; start_segno = cpc.trim_end + 1) {
> >>> - cpc.trim_start = start_segno;
> >>> -
> >>> - if (sbi->discard_blks == 0)
> >>> - break;
> >>> - else if (sbi->discard_blks < BATCHED_TRIM_BLOCKS(sbi))
> >>> - cpc.trim_end = end_segno;
> >>> - else
> >>> - cpc.trim_end = min_t(unsigned int,
> >>> - rounddown(start_segno +
> >>> - BATCHED_TRIM_SEGMENTS(sbi),
> >>> - sbi->segs_per_sec) - 1, end_segno);
> >>> -
> >>> - mutex_lock(&sbi->gc_mutex);
> >>> - err = write_checkpoint(sbi, &cpc);
> >>> - mutex_unlock(&sbi->gc_mutex);
> >>> - if (err)
> >>> - break;
> >>> -
> >>> - schedule();
> >>> - }
> >>> + mutex_lock(&sbi->gc_mutex);
> >>> + err = write_checkpoint(sbi, &cpc);
> >>> + mutex_unlock(&sbi->gc_mutex);
> >>> out:
> >>> range->len = F2FS_BLK_TO_BYTES(cpc.trimmed);
> >>> return err;
> >>> @@ -2708,8 +2698,6 @@ int build_segment_manager(struct f2fs_sb_info *sbi)
> >>> sm_info->nr_discards = 0;
> >>> sm_info->max_discards = 0;
> >>>
> >>> - sm_info->trim_sections = DEF_BATCHED_TRIM_SECTIONS;
> >>> -
> >>> INIT_LIST_HEAD(&sm_info->sit_entry_set);
> >>>
> >>> if (test_opt(sbi, FLUSH_MERGE) && !f2fs_readonly(sbi->sb)) {
> >>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> >>> index 461c29043aec..37d40d8aa9c4 100644
> >>> --- a/fs/f2fs/super.c
> >>> +++ b/fs/f2fs/super.c
> >>> @@ -284,7 +284,6 @@ F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_no_gc_sleep_time, no_gc_sleep_time);
> >>> F2FS_RW_ATTR(GC_THREAD, f2fs_gc_kthread, gc_idle, gc_idle);
> >>> F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, reclaim_segments, rec_prefree_segments);
> >>> F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, max_small_discards, max_discards);
> >>> -F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, batched_trim_sections, trim_sections);
> >>> F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, ipu_policy, ipu_policy);
> >>> F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, min_ipu_util, min_ipu_util);
> >>> F2FS_RW_ATTR(SM_INFO, f2fs_sm_info, min_fsync_blocks, min_fsync_blocks);
> >>> @@ -309,7 +308,6 @@ static struct attribute *f2fs_attrs[] = {
> >>> ATTR_LIST(gc_idle),
> >>> ATTR_LIST(reclaim_segments),
> >>> ATTR_LIST(max_small_discards),
> >>> - ATTR_LIST(batched_trim_sections),
> >>> ATTR_LIST(ipu_policy),
> >>> ATTR_LIST(min_ipu_util),
> >>> ATTR_LIST(min_fsync_blocks),
> >>>
> >>
> >>
> >> ------------------------------------------------------------------------------
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> >> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> >
> > .
> >
>
>
> ------------------------------------------------------------------------------
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