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SubjectRe: [PATCH v2] f2fs: split discard command in prior to block layer
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Hi Jaegeuk,

On 2018/7/15 9:27, Jaegeuk Kim wrote:
> On 07/08, Chao Yu wrote:
>> From: Chao Yu <yuchao0@huawei.com>
>>
>> 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@huawei.com>
>> ---
>> 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,
>> }
>> }
>>
>> -
>> +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);
>> + return;
>> + }
>> + lstart += len;
>> + start += len;
>> + total_len -= len;
>> + len = total_len;
>> + (*issued)++;
>> +
>> + if (len) {
>> + __update_discard_tree_range(sbi, bdev, lstart,
>> + start, len);
>> + dc = (struct discard_cmd *)f2fs_lookup_rb_tree(
>> + &dcc->root, NULL, lstart);
>> + f2fs_bug_on(sbi, !dc);
>> }
>> - } else {
>> - __remove_discard_cmd(sbi, dc);
>> }
>> +
>> + return;
>> }
>>
>> 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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