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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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> >> _______________________________________________
> >> Linux-f2fs-devel mailing list
> >> Linux-f2fs-devel@...ts.sourceforge.net
> >> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> > 
> > .
> > 
> 
> 
> ------------------------------------------------------------------------------
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