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Date: Thu, 24 May 2018 23:18:51 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <yuchao0@...wei.com>
Cc: linux-kernel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH] f2fs: let fstrim issue discard commands in lower priority
On 05/25, Chao Yu wrote:
> Hi Jaegeuk,
>
> On 2018/5/25 13:10, Jaegeuk Kim wrote:
> > The fstrim gathers huge number of large discard commands, and tries to issue
> > without IO awareness, which results in long user-perceive IO latencies on
> > READ, WRITE, and FLUSH in UFS. We've observed some of commands take several
> > seconds due to long discard latency.
> >
> > This patch limits the maximum size to 2MB per candidate, and check IO congestion
> > when issuing them to disk.
> >
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > ---
> > fs/f2fs/f2fs.h | 4 +-
> > fs/f2fs/segment.c | 123 +++++++++++++++++++++++-----------------------
> > 2 files changed, 64 insertions(+), 63 deletions(-)
> >
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 3bddf13794d9..75ae7fc86ae8 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -178,6 +178,7 @@ enum {
> >
> > #define MAX_DISCARD_BLOCKS(sbi) BLKS_PER_SEC(sbi)
> > #define DEF_MAX_DISCARD_REQUEST 8 /* issue 8 discards per round */
> > +#define DEF_MAX_DISCARD_LEN 512 /* Max. 2MB per discard */
> > #define DEF_MIN_DISCARD_ISSUE_TIME 50 /* 50 ms, if exists */
> > #define DEF_MID_DISCARD_ISSUE_TIME 500 /* 500 ms, if device busy */
> > #define DEF_MAX_DISCARD_ISSUE_TIME 60000 /* 60 s, if no candidates */
> > @@ -698,7 +699,8 @@ static inline void set_extent_info(struct extent_info *ei, unsigned int fofs,
> > static inline bool __is_discard_mergeable(struct discard_info *back,
> > struct discard_info *front)
> > {
> > - return back->lstart + back->len == front->lstart;
> > + return (back->lstart + back->len == front->lstart) &&
> > + (back->len + front->len < DEF_MAX_DISCARD_LEN);
> > }
> >
> > static inline bool __is_discard_back_mergeable(struct discard_info *cur,
> > diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> > index 843fc2e6d41c..ba996d4091bc 100644
> > --- a/fs/f2fs/segment.c
> > +++ b/fs/f2fs/segment.c
> > @@ -1139,68 +1139,6 @@ static int __queue_discard_cmd(struct f2fs_sb_info *sbi,
> > return 0;
> > }
> >
> > -static void __issue_discard_cmd_range(struct f2fs_sb_info *sbi,
> > - struct discard_policy *dpolicy,
> > - unsigned int start, unsigned int end)
> > -{
> > - struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> > - struct discard_cmd *prev_dc = NULL, *next_dc = NULL;
> > - struct rb_node **insert_p = NULL, *insert_parent = NULL;
> > - struct discard_cmd *dc;
> > - struct blk_plug plug;
> > - int issued;
> > -
> > -next:
> > - issued = 0;
> > -
> > - mutex_lock(&dcc->cmd_lock);
> > - f2fs_bug_on(sbi, !__check_rb_tree_consistence(sbi, &dcc->root));
> > -
> > - dc = (struct discard_cmd *)__lookup_rb_tree_ret(&dcc->root,
> > - NULL, start,
> > - (struct rb_entry **)&prev_dc,
> > - (struct rb_entry **)&next_dc,
> > - &insert_p, &insert_parent, true);
> > - if (!dc)
> > - dc = next_dc;
> > -
> > - blk_start_plug(&plug);
> > -
> > - while (dc && dc->lstart <= end) {
> > - struct rb_node *node;
> > -
> > - if (dc->len < dpolicy->granularity)
> > - goto skip;
> > -
> > - if (dc->state != D_PREP) {
> > - list_move_tail(&dc->list, &dcc->fstrim_list);
> > - goto skip;
> > - }
> > -
> > - __submit_discard_cmd(sbi, dpolicy, dc);
> > -
> > - if (++issued >= dpolicy->max_requests) {
> > - start = dc->lstart + dc->len;
> > -
> > - blk_finish_plug(&plug);
> > - mutex_unlock(&dcc->cmd_lock);
> > -
> > - schedule();
> > -
> > - goto next;
> > - }
> > -skip:
> > - node = rb_next(&dc->rb_node);
> > - dc = rb_entry_safe(node, struct discard_cmd, rb_node);
> > -
> > - if (fatal_signal_pending(current))
> > - break;
> > - }
> > -
> > - blk_finish_plug(&plug);
> > - mutex_unlock(&dcc->cmd_lock);
> > -}
> > -
> > static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> > struct discard_policy *dpolicy)
> > {
> > @@ -2397,6 +2335,67 @@ bool exist_trim_candidates(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> > return has_candidate;
> > }
> >
> > +static void __issue_discard_cmd_range(struct f2fs_sb_info *sbi,
> > + struct discard_policy *dpolicy,
> > + unsigned int start, unsigned int end)
> > +{
> > + struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> > + struct discard_cmd *prev_dc = NULL, *next_dc = NULL;
> > + struct rb_node **insert_p = NULL, *insert_parent = NULL;
> > + struct discard_cmd *dc;
> > + struct blk_plug plug;
> > + int issued;
>
> unsigned int cur = start;
>
> > +
> > +next:
> > + issued = 0;
> > +
> > + mutex_lock(&dcc->cmd_lock);
> > + f2fs_bug_on(sbi, !__check_rb_tree_consistence(sbi, &dcc->root));
> > +
> > + dc = (struct discard_cmd *)__lookup_rb_tree_ret(&dcc->root,
> > + NULL, start,
>
> NULL, cur,
>
> > + (struct rb_entry **)&prev_dc,
> > + (struct rb_entry **)&next_dc,
> > + &insert_p, &insert_parent, true);
> > + if (!dc)
> > + dc = next_dc;
> > +
> > + blk_start_plug(&plug);
> > +
> > + while (dc && dc->lstart <= end) {
> > + struct rb_node *node;
> > +
> > + if (dc->len < dpolicy->granularity)
> > + goto skip;
> > +
> > + if (dc->state != D_PREP) {
> > + list_move_tail(&dc->list, &dcc->fstrim_list);
> > + goto skip;
> > + }
> > +
> > + __submit_discard_cmd(sbi, dpolicy, dc);
> > +
> > + if (++issued >= dpolicy->max_requests) {
> > + start = dc->lstart + dc->len;
>
> cur = dc->lstart + dc->len;
>
> > +
> > + blk_finish_plug(&plug);
> > + mutex_unlock(&dcc->cmd_lock);
> > + __wait_all_discard_cmd(sbi, dpolicy);
>
> How about moving __wait_discard_cmd_range(sbi, &dpolicy, start, end) from
> f2fs_trim_fs here, this can avoid wait non-fstrim discard commands.
The key here is to avoid any outstanding discard commands.
>
> > + congestion_wait(BLK_RW_ASYNC, HZ/50);
>
> What about using msleep(dpolicy->min_interval) instead?
We need to detect congestion in block layer.
Thanks,
>
> Thanks,
>
> > + goto next;
> > + }
> > +skip:
> > + node = rb_next(&dc->rb_node);
> > + dc = rb_entry_safe(node, struct discard_cmd, rb_node);
> > +
> > + if (fatal_signal_pending(current))
> > + break;
> > + }
> > +
> > + blk_finish_plug(&plug);
> > + mutex_unlock(&dcc->cmd_lock);
> > +}
> > +
> > int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
> > {
> > __u64 start = F2FS_BYTES_TO_BLK(range->start);
> >
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