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Date: Fri, 25 May 2018 14:47:12 +0800
From: Chao Yu <yuchao0@...wei.com>
To: Jaegeuk Kim <jaegeuk@...nel.org>
CC: <linux-kernel@...r.kernel.org>,
<linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [PATCH] f2fs: let fstrim issue discard commands in lower priority
On 2018/5/25 14:18, Jaegeuk Kim wrote:
> On 05/25, Chao Yu wrote:
>> Hi Jaegeuk,
>>
>> On 2018/5/25 13:10, Jaegeuk Kim wrote:
>>> The fstrim gathers huge number of large discard commands, and tries to issue
>>> without IO awareness, which results in long user-perceive IO latencies on
>>> READ, WRITE, and FLUSH in UFS. We've observed some of commands take several
>>> seconds due to long discard latency.
>>>
>>> This patch limits the maximum size to 2MB per candidate, and check IO congestion
>>> when issuing them to disk.
>>>
>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
>>> ---
>>> fs/f2fs/f2fs.h | 4 +-
>>> fs/f2fs/segment.c | 123 +++++++++++++++++++++++-----------------------
>>> 2 files changed, 64 insertions(+), 63 deletions(-)
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index 3bddf13794d9..75ae7fc86ae8 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -178,6 +178,7 @@ 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 */
>>> @@ -698,7 +699,8 @@ 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)
>>> {
>>> - return back->lstart + back->len == front->lstart;
>>> + return (back->lstart + back->len == front->lstart) &&
>>> + (back->len + front->len < DEF_MAX_DISCARD_LEN);
>>> }
>>>
>>> static inline bool __is_discard_back_mergeable(struct discard_info *cur,
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index 843fc2e6d41c..ba996d4091bc 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -1139,68 +1139,6 @@ static int __queue_discard_cmd(struct f2fs_sb_info *sbi,
>>> return 0;
>>> }
>>>
>>> -static void __issue_discard_cmd_range(struct f2fs_sb_info *sbi,
>>> - struct discard_policy *dpolicy,
>>> - unsigned int start, unsigned int end)
>>> -{
>>> - struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>>> - struct discard_cmd *prev_dc = NULL, *next_dc = NULL;
>>> - struct rb_node **insert_p = NULL, *insert_parent = NULL;
>>> - struct discard_cmd *dc;
>>> - struct blk_plug plug;
>>> - int issued;
>>> -
>>> -next:
>>> - issued = 0;
>>> -
>>> - mutex_lock(&dcc->cmd_lock);
>>> - f2fs_bug_on(sbi, !__check_rb_tree_consistence(sbi, &dcc->root));
>>> -
>>> - dc = (struct discard_cmd *)__lookup_rb_tree_ret(&dcc->root,
>>> - NULL, start,
>>> - (struct rb_entry **)&prev_dc,
>>> - (struct rb_entry **)&next_dc,
>>> - &insert_p, &insert_parent, true);
>>> - if (!dc)
>>> - dc = next_dc;
>>> -
>>> - blk_start_plug(&plug);
>>> -
>>> - while (dc && dc->lstart <= end) {
>>> - struct rb_node *node;
>>> -
>>> - if (dc->len < dpolicy->granularity)
>>> - goto skip;
>>> -
>>> - if (dc->state != D_PREP) {
>>> - list_move_tail(&dc->list, &dcc->fstrim_list);
>>> - goto skip;
>>> - }
>>> -
>>> - __submit_discard_cmd(sbi, dpolicy, dc);
>>> -
>>> - if (++issued >= dpolicy->max_requests) {
>>> - start = dc->lstart + dc->len;
>>> -
>>> - blk_finish_plug(&plug);
>>> - mutex_unlock(&dcc->cmd_lock);
>>> -
>>> - schedule();
>>> -
>>> - goto next;
>>> - }
>>> -skip:
>>> - node = rb_next(&dc->rb_node);
>>> - dc = rb_entry_safe(node, struct discard_cmd, rb_node);
>>> -
>>> - if (fatal_signal_pending(current))
>>> - break;
>>> - }
>>> -
>>> - blk_finish_plug(&plug);
>>> - mutex_unlock(&dcc->cmd_lock);
>>> -}
>>> -
>>> static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>>> struct discard_policy *dpolicy)
>>> {
>>> @@ -2397,6 +2335,67 @@ bool exist_trim_candidates(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>>> return has_candidate;
>>> }
>>>
>>> +static void __issue_discard_cmd_range(struct f2fs_sb_info *sbi,
>>> + struct discard_policy *dpolicy,
>>> + unsigned int start, unsigned int end)
>>> +{
>>> + struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>>> + struct discard_cmd *prev_dc = NULL, *next_dc = NULL;
>>> + struct rb_node **insert_p = NULL, *insert_parent = NULL;
>>> + struct discard_cmd *dc;
>>> + struct blk_plug plug;
>>> + int issued;
>>
>> unsigned int cur = start;
>>
>>> +
>>> +next:
>>> + issued = 0;
>>> +
>>> + mutex_lock(&dcc->cmd_lock);
>>> + f2fs_bug_on(sbi, !__check_rb_tree_consistence(sbi, &dcc->root));
>>> +
>>> + dc = (struct discard_cmd *)__lookup_rb_tree_ret(&dcc->root,
>>> + NULL, start,
>>
>> NULL, cur,
>>
>>> + (struct rb_entry **)&prev_dc,
>>> + (struct rb_entry **)&next_dc,
>>> + &insert_p, &insert_parent, true);
>>> + if (!dc)
>>> + dc = next_dc;
>>> +
>>> + blk_start_plug(&plug);
>>> +
>>> + while (dc && dc->lstart <= end) {
>>> + struct rb_node *node;
>>> +
>>> + if (dc->len < dpolicy->granularity)
>>> + goto skip;
>>> +
>>> + if (dc->state != D_PREP) {
>>> + list_move_tail(&dc->list, &dcc->fstrim_list);
>>> + goto skip;
>>> + }
>>> +
>>> + __submit_discard_cmd(sbi, dpolicy, dc);
>>> +
>>> + if (++issued >= dpolicy->max_requests) {
>>> + start = dc->lstart + dc->len;
>>
>> cur = dc->lstart + dc->len;
>>
>>> +
>>> + blk_finish_plug(&plug);
>>> + mutex_unlock(&dcc->cmd_lock);
>>> + __wait_all_discard_cmd(sbi, dpolicy);
>>
>> How about moving __wait_discard_cmd_range(sbi, &dpolicy, start, end) from
>> f2fs_trim_fs here, this can avoid wait non-fstrim discard commands.
Sorry, in fstrim, __wait_all_discard_cmd already just wait discard commands
which are issued by itself.
>
> The key here is to avoid any outstanding discard commands.
You want to wait all in-flight discard commands? So we need to wrap one other
function for that.
static void wait_all_discard_cmd(struct f2fs_sb_info *sbi,
struct discard_policy *dpolicy, bool wait_all)
{
if (dpolicy->type == DPOLICY_FSTRIM || wait_all)
__wait_discard_cmd_range(sbi, dpolicy, dcc->fstrim_list);
if (dpolicy->type != DPOLICY_FSTRIM || wait_all)
__wait_discard_cmd_range(sbi, dpolicy, dcc->wait_list);
}
>
>>
>>> + congestion_wait(BLK_RW_ASYNC, HZ/50);
>>
>> What about using msleep(dpolicy->min_interval) instead?
>
> We need to detect congestion in block layer.
OK.
Thanks,
>
> Thanks,
>
>>
>> Thanks,
>>
>>> + goto next;
>>> + }
>>> +skip:
>>> + node = rb_next(&dc->rb_node);
>>> + dc = rb_entry_safe(node, struct discard_cmd, rb_node);
>>> +
>>> + if (fatal_signal_pending(current))
>>> + break;
>>> + }
>>> +
>>> + blk_finish_plug(&plug);
>>> + mutex_unlock(&dcc->cmd_lock);
>>> +}
>>> +
>>> int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
>>> {
>>> __u64 start = F2FS_BYTES_TO_BLK(range->start);
>>>
>
> .
>
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