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Message-ID: <1baedfdd-f96e-2250-7623-ec4385b3eb62@kernel.org>
Date: Mon, 23 Jul 2018 21:22:14 +0800
From: Chao Yu <chao@...nel.org>
To: Jaegeuk Kim <jaegeuk@...nel.org>
Cc: linux-kernel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: split discard command in prior to
block layer
On 2018/7/23 20:47, Jaegeuk Kim wrote:
> 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@...wei.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@...wei.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,
>>>>>> }
>>>>>> }
>>>>>>
>>>>>> -
>>>
>>> ===================== 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?
Got you, let me try to refactor a bit for that.
Thanks,
>
> 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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