lkml.org 
[lkml]   [2018]   [Jul]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] f2fs: give another chance to issue discard with current granularity
On 07/07, Chao Yu wrote:
> Hi Jaegeuk,
>
> On 2018/7/7 6:49, Jaegeuk Kim wrote:
> > On 07/05, Chao Yu wrote:
> >> If discard IOs are blocked by user IO, do not skip to select and issue
> >> discard with lower granularity, retry with current granularity.
> >
> > We need to stop as soon as possible since user activity comes. Later, discard
> > thread will try it again in another idle time. What's your concern?
>
> Currently, our implementation is that we will try to issue
> DEF_MAX_DISCARD_REQUEST discards as many as possible in batch, for example:
>
> If there is 4 discard entry in rb-tree, we will try to issue them by below order
> in batch:
>
> No. size is_idle op
> #1 discard 2MB false skip
> #2 discard 2MB false skip
> #3 discard 256KB true issue
> #4 discard 16KB true issue
>
> So if is_idle is false temporarily, we can still have chance to issue #3 & #4
> discard in this round once is_idle is flipped?
>
> But the problem is we skip issue discard with big granularity, so I add this
> patch to do retry with current granularity.
>
> Do you mean that we need to stop issuing discard immediately once we detect IO
> is busy?

Yes. If we retry to issue discard continuously, it hurts normal IO latencies.

>
> Thanks,
>
> >
> >>
> >> Signed-off-by: Chao Yu <yuchao0@huawei.com>
> >> ---
> >> v2:
> >> - fix deadloop.
> >> fs/f2fs/segment.c | 16 +++++++++++++---
> >> 1 file changed, 13 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >> index 1f9ae8270f86..6e2b2e717a40 100644
> >> --- a/fs/f2fs/segment.c
> >> +++ b/fs/f2fs/segment.c
> >> @@ -1191,7 +1191,7 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >> struct discard_cmd *dc, *tmp;
> >> struct blk_plug plug;
> >> int i, iter = 0, issued = 0;
> >> - bool io_interrupted = false;
> >> + bool io_interrupted = false, end_up = false;
> >>
> >> for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
> >> if (i + 1 < dpolicy->granularity)
> >> @@ -1199,6 +1199,7 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >> pend_list = &dcc->pend_list[i];
> >>
> >> mutex_lock(&dcc->cmd_lock);
> >> +retry:
> >> if (list_empty(pend_list))
> >> goto next;
> >> if (unlikely(dcc->rbtree_check))
> >> @@ -1217,14 +1218,23 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
> >> __submit_discard_cmd(sbi, dpolicy, dc);
> >> issued++;
> >> skip:
> >> - if (++iter >= dpolicy->max_requests)
> >> + if (++iter >= dpolicy->max_requests) {
> >> + end_up = true;
> >> break;
> >> + }
> >> }
> >> blk_finish_plug(&plug);
> >> +
> >> + /*
> >> + * if discard IO was interrupted by user IOs, give another
> >> + * chance to issue discard with current granularity.
> >> + */
> >> + if (io_interrupted && !end_up)
> >> + goto retry;
> >> next:
> >> mutex_unlock(&dcc->cmd_lock);
> >>
> >> - if (iter >= dpolicy->max_requests)
> >> + if (end_up)
> >> break;
> >> }
> >>
> >> --
> >> 2.18.0.rc1

\
 
 \ /
  Last update: 2018-07-07 03:11    [W:0.042 / U:0.076 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site