Messages in this thread | | | Date | Fri, 6 Jul 2018 18:10:12 -0700 | From | Jaegeuk Kim <> | Subject | Re: [PATCH v2] f2fs: give another chance to issue discard with current granularity |
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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
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