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

Chao Yu
2018-07-06T23:35:41Z

Hi Jaegeuk,

On 2018/7/7 6:45, Jaegeuk Kim wrote:
> On 07/04, 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.
>
> Hi Chao,
>
> In terms of # of candidates, can we control this when actually issuing
> the discard commands?

IIUC, you mean once we pick one discard entry in rbtree, if
max_{hw,}discard_sectors is smaller than size of this discard, then we can split
it into smaller ones by discard_sectors, and just issue one or partials of them?

Thanks,

>
> Thanks,
>
>>
>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>> ---
>> fs/f2fs/f2fs.h | 13 ++++++-------
>> fs/f2fs/segment.c | 25 ++++++++++++++++++++++---
>> 2 files changed, 28 insertions(+), 10 deletions(-)
>>
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> index a9da5a089cb4..a09d2b2d9520 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 */
>> @@ -701,22 +700,22 @@ 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 4648561e2bfd..8e417a12684d 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -1086,6 +1086,9 @@ 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);
>> @@ -1129,7 +1132,8 @@ 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);
>> @@ -1140,7 +1144,8 @@ 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;
>> @@ -1170,7 +1175,11 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
>> static int __queue_discard_cmd(struct f2fs_sb_info *sbi,
>> struct block_device *bdev, block_t blkstart, block_t blklen)
>> {
>> + struct request_queue *q = bdev_get_queue(bdev);
>> + unsigned int max_discard_blocks =
>> + SECTOR_TO_BLOCK(q->limits.max_discard_sectors);
>> block_t lblkstart = blkstart;
>> + block_t total_len = blklen;
>>
>> trace_f2fs_queue_discard(bdev, blkstart, blklen);
>>
>> @@ -1179,7 +1188,17 @@ static int __queue_discard_cmd(struct f2fs_sb_info *sbi,
>>
>> blkstart -= FDEV(devi).start_blk;
>> }
>> - __update_discard_tree_range(sbi, bdev, lblkstart, blkstart, blklen);
>> +
>> + while (total_len) {
>> + if (blklen > max_discard_blocks)
>> + blklen = max_discard_blocks;
>> + __update_discard_tree_range(sbi, bdev, lblkstart,
>> + blkstart, blklen);
>> + lblkstart += blklen;
>> + blkstart += blklen;
>> + total_len -= blklen;
>> + blklen = total_len;
>> + }
>> return 0;
>> }
>>
>> --
>> 2.16.2.17.g38e79b1fd