Re: [PATCH v2] f2fs: split discard command in prior to block layer

From: Jaegeuk Kim
Date: Mon Jul 23 2018 - 08:47:53 EST

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On 07/15, Chao Yu wrote:
> On 2018/7/15 11:13, Jaegeuk Kim wrote:
> > On 07/15, Chao Yu wrote:
> >> Hi Jaegeuk,
> >>
> >> On 2018/7/15 9:27, Jaegeuk Kim wrote:
> >>> On 07/08, Chao Yu wrote:
> >>>> From: Chao Yu <yuchao0@xxxxxxxxxx>
> >>>>
> >>>> Some devices has small max_{hw,}discard_sectors, so that in
> >>>> __blkdev_issue_discard(), one big size discard bio can be split
> >>>> into multiple small size discard bios, result in heavy load in IO
> >>>> scheduler and device, which can hang other sync IO for long time.
> >>>>
> >>>> Now, f2fs is trying to control discard commands more elaboratively,
> >>>> in order to make less conflict in between discard IO and user IO
> >>>> to enhance application's performance, so in this patch, we will
> >>>> split discard bio in f2fs in prior to in block layer to reduce
> >>>> issuing multiple discard bios in a short time.
> >>>
> >>> Can we just change __submit_discard_cmd() to submit the large candidate
> >>> partially and adjust lstart in the original candidate?
> >>
> >> Yep, could you check __submit_discard_cmd() implementation below? Does that
> >> match the thoughts from you?
> >>
> >> Thanks,
> >>
> >>>
> >>>>
> >>>> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
> >>>> ---
> >>>> v2:
> >>>> - change to split discard command entry before submission.
> >>>> fs/f2fs/f2fs.h | 13 +++---
> >>>> fs/f2fs/segment.c | 117 +++++++++++++++++++++++++++++++++++++-----------------
> >>>> 2 files changed, 86 insertions(+), 44 deletions(-)
> >>>>
> >>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >>>> index c48b655d5d8d..359526d88d3f 100644
> >>>> --- a/fs/f2fs/f2fs.h
> >>>> +++ b/fs/f2fs/f2fs.h
> >>>> @@ -178,7 +178,6 @@ 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 */
> >>>> @@ -709,22 +708,22 @@ 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)
> >>>> + struct discard_info *front, unsigned int max_len)
> >>>> {
> >>>> return (back->lstart + back->len == front->lstart) &&
> >>>> - (back->len + front->len < DEF_MAX_DISCARD_LEN);
> >>>> + (back->len + front->len <= max_len);
> >>>> }
> >>>>
> >>>> static inline bool __is_discard_back_mergeable(struct discard_info *cur,
> >>>> - struct discard_info *back)
> >>>> + struct discard_info *back, unsigned int max_len)
> >>>> {
> >>>> - return __is_discard_mergeable(back, cur);
> >>>> + return __is_discard_mergeable(back, cur, max_len);
> >>>> }
> >>>>
> >>>> static inline bool __is_discard_front_mergeable(struct discard_info *cur,
> >>>> - struct discard_info *front)
> >>>> + struct discard_info *front, unsigned int max_len)
> >>>> {
> >>>> - return __is_discard_mergeable(cur, front);
> >>>> + return __is_discard_mergeable(cur, front, max_len);
> >>>> }
> >>>>
> >>>> static inline bool __is_extent_mergeable(struct extent_info *back,
> >>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>>> index f7f56dd091b4..cbf8f3f9a8e7 100644
> >>>> --- a/fs/f2fs/segment.c
> >>>> +++ b/fs/f2fs/segment.c
> >>>> @@ -966,17 +966,24 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi,
> >>>> }
> >>>> }
> >>>>
> >>>> -
> >
> > ===================== BEGIN
> >
> >>>> +static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
> >>>> + struct block_device *bdev, block_t lstart,
> >>>> + block_t start, block_t len);
> >>>> /* this function is copied from blkdev_issue_discard from block/blk-lib.c */
> >>>> static void __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >>>> struct discard_policy *dpolicy,
> >>>> - struct discard_cmd *dc)
> >>>> + struct discard_cmd *dc,
> >>>> + unsigned int *issued)
> >>>> {
> >>>> + struct block_device *bdev = dc->bdev;
> >>>> + struct request_queue *q = bdev_get_queue(bdev);
> >>>> + unsigned int max_discard_blocks =
> >>>> + SECTOR_TO_BLOCK(q->limits.max_discard_sectors);
> >>>> struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> >>>> struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
> >>>> &(dcc->fstrim_list) : &(dcc->wait_list);
> >>>> - struct bio *bio = NULL;
> >>>> int flag = dpolicy->sync ? REQ_SYNC : 0;
> >>>> + block_t lstart, start, len, total_len;
> >>>>
> >>>> if (dc->state != D_PREP)
> >>>> return;
> >>>> @@ -984,30 +991,63 @@ static void __submit_discard_cmd(struct f2fs_sb_info *sbi,
> >>>> if (is_sbi_flag_set(sbi, SBI_NEED_FSCK))
> >>>> return;
> >>>>
> >>>> - trace_f2fs_issue_discard(dc->bdev, dc->start, dc->len);
> >>>> -
> >>>> - dc->error = __blkdev_issue_discard(dc->bdev,
> >>>> - SECTOR_FROM_BLOCK(dc->start),
> >>>> - SECTOR_FROM_BLOCK(dc->len),
> >>>> - GFP_NOFS, 0, &bio);
> >>>> - if (!dc->error) {
> >>>> - /* should keep before submission to avoid D_DONE right away */
> >>>> - dc->state = D_SUBMIT;
> >>>> - atomic_inc(&dcc->issued_discard);
> >>>> - atomic_inc(&dcc->issing_discard);
> >>>> - if (bio) {
> >>>> - bio->bi_private = dc;
> >>>> - bio->bi_end_io = f2fs_submit_discard_endio;
> >>>> - bio->bi_opf |= flag;
> >>>> - submit_bio(bio);
> >>>> - list_move_tail(&dc->list, wait_list);
> >>>> - __check_sit_bitmap(sbi, dc->start, dc->start + dc->len);
> >>>> -
> >>>> - f2fs_update_iostat(sbi, FS_DISCARD, 1);
> >>>> + trace_f2fs_issue_discard(bdev, dc->start, dc->len);
> >>>> +
> >>>> + lstart = dc->lstart;
> >>>> + start = dc->start;
> >>>> + len = dc->len;
> >>>> + total_len = len;
> >>>> +
> >>>> + while (total_len && *issued < dpolicy->max_requests) {
> >>>> + struct bio *bio = NULL;
> >>>> +
> >>>> + if (len > max_discard_blocks)
> >>>> + len = max_discard_blocks;
> >>>> +
> >>>> + dc->error = __blkdev_issue_discard(bdev,
> >>>> + SECTOR_FROM_BLOCK(start),
> >>>> + SECTOR_FROM_BLOCK(len),
> >>>> + GFP_NOFS, 0, &bio);
> >>>> + if (!dc->error) {
> >>>> + /*
> >>>> + * should keep before submission to avoid D_DONE
> >>>> + * right away
> >>>> + */
> >>>> + dc->state = D_SUBMIT;
> >>>> + dc->len = len;
> >>>> + atomic_inc(&dcc->issued_discard);
> >>>> + atomic_inc(&dcc->issing_discard);
> >>>> + if (bio) {
> >>>> + bio->bi_private = dc;
> >>>> + bio->bi_end_io = f2fs_submit_discard_endio;
> >>>> + bio->bi_opf |= flag;
> >>>> + submit_bio(bio);
> >>>> + list_move_tail(&dc->list, wait_list);
> >>>> + __check_sit_bitmap(sbi, dc->start,
> >>>> + dc->start + dc->len);
> >>>> +
> >>>> + f2fs_update_iostat(sbi, FS_DISCARD, 1);
> >>>> + }
> >>>> + } else {
> >>>> + __remove_discard_cmd(sbi, dc);
> >
> > Keep the original one, since it's partially failed?
>
> During __submit_discard_cmd(), we are trying to split original dc into multiple
> dc, and once we failed to submit some of them, we will remove corresponding dc,
> the removal logic is the same as before, not being changed...
>
> If we want to keep failed dc and do retry, we'd better add another patch for
> that, right?

I thought removing failed portion of the dc.

>
> >
> >>>> + return;
> >>>> + }
> >>>> + lstart += len;
> >>>> + start += len;
> >>>> + total_len -= len;
> >>>> + len = total_len;
> >>>> + (*issued)++;
> >>>> +
> >>>> + if (len) {
> >>>> + __update_discard_tree_range(sbi, bdev, lstart,
> >>>> + start, len);
> >
> > Do we really need this? We already grabbed one candidate which was not merged
> > well.
>
> You mean submitting multiple bios based on one large size dc?

Yes.

>
> Previously, one bio references to one dc as below, in end_io, it will change
> dc->state which can be detected by its own waiter.
>
> bio->bi_private = dc;
> bio->bi_end_io = f2fs_submit_discard_endio;
> bio->bi_opf |= flag;
>
> If multiple bios reference to one dc, it will be more complicated to handle
> that. How do you think?

I was concerned about too many entries in the lists. How about adding a refcnt
to count how many bios were issued on the dc?

Thanks,

>
> Thanks,
>
> >
> >>>> + dc = (struct discard_cmd *)f2fs_lookup_rb_tree(
> >>>> + &dcc->root, NULL, lstart);
> >>>> + f2fs_bug_on(sbi, !dc);
> >>>> }
> >>>> - } else {
> >>>> - __remove_discard_cmd(sbi, dc);
> >>>> }
> >>>> +
> >>>> + return;
> >>>> }
> >
> > ======================= END
> >
> >
> >>>>
> >>>> static struct discard_cmd *__insert_discard_tree(struct f2fs_sb_info *sbi,
> >>>> @@ -1088,10 +1128,11 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
> >>>> struct discard_cmd *dc;
> >>>> struct discard_info di = {0};
> >>>> struct rb_node **insert_p = NULL, *insert_parent = NULL;
> >>>> + struct request_queue *q = bdev_get_queue(bdev);
> >>>> + unsigned int max_discard_blocks =
> >>>> + SECTOR_TO_BLOCK(q->limits.max_discard_sectors);
> >>>> block_t end = lstart + len;
> >>>>
> >>>> - mutex_lock(&dcc->cmd_lock);
> >>>> -
> >>>> dc = (struct discard_cmd *)f2fs_lookup_rb_tree_ret(&dcc->root,
> >>>> NULL, lstart,
> >>>> (struct rb_entry **)&prev_dc,
> >>>> @@ -1131,7 +1172,8 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
> >>>>
> >>>> if (prev_dc && prev_dc->state == D_PREP &&
> >>>> prev_dc->bdev == bdev &&
> >>>> - __is_discard_back_mergeable(&di, &prev_dc->di)) {
> >>>> + __is_discard_back_mergeable(&di, &prev_dc->di,
> >>>> + max_discard_blocks)) {
> >>>> prev_dc->di.len += di.len;
> >>>> dcc->undiscard_blks += di.len;
> >>>> __relocate_discard_cmd(dcc, prev_dc);
> >>>> @@ -1142,7 +1184,8 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
> >>>>
> >>>> if (next_dc && next_dc->state == D_PREP &&
> >>>> next_dc->bdev == bdev &&
> >>>> - __is_discard_front_mergeable(&di, &next_dc->di)) {
> >>>> + __is_discard_front_mergeable(&di, &next_dc->di,
> >>>> + max_discard_blocks)) {
> >>>> next_dc->di.lstart = di.lstart;
> >>>> next_dc->di.len += di.len;
> >>>> next_dc->di.start = di.start;
> >>>> @@ -1165,8 +1208,6 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
> >>>> node = rb_next(&prev_dc->rb_node);
> >>>> next_dc = rb_entry_safe(node, struct discard_cmd, rb_node);
> >>>> }
> >>>> -
> >>>> - mutex_unlock(&dcc->cmd_lock);
> >>>> }
> >>>>
> >>>> static int __queue_discard_cmd(struct f2fs_sb_info *sbi,
> >>>> @@ -1181,7 +1222,9 @@ static int __queue_discard_cmd(struct f2fs_sb_info *sbi,
> >>>>
> >>>> blkstart -= FDEV(devi).start_blk;
> >>>> }
> >>>> + mutex_lock(&SM_I(sbi)->dcc_info->cmd_lock);
> >>>> __update_discard_tree_range(sbi, bdev, lblkstart, blkstart, blklen);
> >>>> + mutex_unlock(&SM_I(sbi)->dcc_info->cmd_lock);
> >>>> return 0;
> >>>> }
> >>>>
> >>>> @@ -1220,9 +1263,9 @@ static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
> >>>> }
> >>>>
> >>>> dcc->next_pos = dc->lstart + dc->len;
> >>>> - __submit_discard_cmd(sbi, dpolicy, dc);
> >>>> + __submit_discard_cmd(sbi, dpolicy, dc, &issued);
> >>>>
> >>>> - if (++issued >= dpolicy->max_requests)
> >>>> + if (issued >= dpolicy->max_requests)
> >>>> break;
> >>>> next:
> >>>> node = rb_next(&dc->rb_node);
> >>>> @@ -1277,9 +1320,9 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >>>> break;
> >>>> }
> >>>>
> >>>> - __submit_discard_cmd(sbi, dpolicy, dc);
> >>>> + __submit_discard_cmd(sbi, dpolicy, dc, &issued);
> >>>>
> >>>> - if (++issued >= dpolicy->max_requests)
> >>>> + if (issued >= dpolicy->max_requests)
> >>>> break;
> >>>> }
> >>>> blk_finish_plug(&plug);
> >>>> @@ -2475,9 +2518,9 @@ static unsigned int __issue_discard_cmd_range(struct f2fs_sb_info *sbi,
> >>>> goto skip;
> >>>> }
> >>>>
> >>>> - __submit_discard_cmd(sbi, dpolicy, dc);
> >>>> + __submit_discard_cmd(sbi, dpolicy, dc, &issued);
> >>>>
> >>>> - if (++issued >= dpolicy->max_requests) {
> >>>> + if (issued >= dpolicy->max_requests) {
> >>>> start = dc->lstart + dc->len;
> >>>>
> >>>> blk_finish_plug(&plug);
> >>>> --
> >>>> 2.16.2.17.g38e79b1fd

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