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

Chao Yu
2018-07-07T01:40:01Z

On 2018/7/7 9:08, Jaegeuk Kim wrote:
> On 07/07, Chao Yu wrote:
>> 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?
>
> Yes, sort of.

Let me try to refactor the patch.

Thanks,

>
>>
>> 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