Hi Chao,
On Mon, Mar 15, 2021 at 04:10:22PM +0800, Chao Yu wrote:
> Hi Sahitya,
>
> On 2021/3/15 15:46, Sahitya Tummala wrote:
> >Hi Chao,
> >
> >On Mon, Mar 15, 2021 at 02:12:44PM +0800, Chao Yu wrote:
> >>Sahitya,
> >>
> >>On 2021/3/15 12:56, Sahitya Tummala wrote:
> >>>When f2fs is heavily utilized over 80%, the current discard policy
> >>>sets the max sleep timeout of discard thread as 50ms
> >>>(DEF_MIN_DISCARD_ISSUE_TIME). But this is set even when there are
> >>>no pending discard commands to be issued. This results into
> >>>unnecessary frequent and periodic wake ups of the discard thread.
> >>>This patch adds check for pending discard commands in addition
> >>>to heavy utilization condition to prevent those wake ups.
> >>
> >>Could this commit fix your issue?
> >>
> >>https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git/commit/?h=dev&id=43f8c47ea7d59c7b2270835f1d7c4618a1ea27b6
> >>
> >I don't think it will help because we are changing the max timeout of the
> >dpolicy itself in __init_discard_policy() when util > 80% as below -
> >
> >dpolicy->max_interval = DEF_MIN_DISCARD_ISSUE_TIME;
> >
> >And issue_discard_thread() uses this value as wait_ms, when there
> >are no more pending discard commands to be issued.
> ><snip>
> > } else {
> > wait_ms = dpolicy.max_interval;
> > }
> ><snip>
> >
> >The new patch posted above is not changing anything related to the
> >max_interval.
> >Hence, I think it won't help the uncessary wakeup problem I am trying to
> >solve
> >for this condition - util > 80% and when there are no pending discards.
> >
> >Please let me know if i am missing something.
>
> Copied, thanks for the explanation.
>
> But there is another case which can cause this issue in the case of
> disk util < 80%.
>
> wait_ms = DEF_MIN_DISCARD_ISSUE_TIME;
>
> do {
> wait_event_interruptible_timeout(, wait_ms);
>
> ...
>
> if (!atomic_read(&dcc->discard_cmd_cnt))
> [1] new statement
> continue;
>
> } while();
>
> Then the loop will wakeup whenever 50ms timeout.
>
Yes, only for a short period of time i.e., until the first discard command
is issued. Once a discard is issued, it will use
wait_ms = dpolicy.max_interval;
> So, to avoid this case, shouldn't we reset wait_ms to dpolicy.max_interval
> at [1]?
>
Yes, we can add that to cover the above case.
> Meanwhile, how about relocating discard_cmd_cnt check after
> __init_discard_policy(DPOLICY_FORCE)? and olny set .max_interval to
> DEF_MAX_DISCARD_ISSUE_TIME if there is no discard command, and keep
> .granularity to 1?
>
There is not need to change .granularity, right? It will be controlled
as per utilization as it is done today. Only max_interval and wait_ms
needs to be updated. Does this look good?
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index d7076796..958ad1e 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1772,13 +1772,16 @@ static int issue_discard_thread(void *data)
wait_ms = dpolicy.max_interval;
continue;
}
- if (!atomic_read(&dcc->discard_cmd_cnt))
- continue;
-
if (sbi->gc_mode == GC_URGENT_HIGH ||
!f2fs_available_free_memory(sbi, DISCARD_CACHE))
__init_discard_policy(sbi, &dpolicy, DPOLICY_FORCE, 1);
+ if (!atomic_read(&dcc->discard_cmd_cnt)) {
+ dpolicy.max_interval = DEF_MAX_DISCARD_ISSUE_TIME;
+ wait_ms = dpolicy.max_interval;
+ continue;
+ }
+
sb_start_intwrite(sbi->sb);
issued = __issue_discard_cmd(sbi, &dpolicy);
thanks,
Sahitya.
> Thanks,
>
> >
> >Thanks,
> >Sahitya.
> >
> >>Thanks,
> >>
> >>>
> >>>Signed-off-by: Sahitya Tummala <stumm...@codeaurora.org>
> >>>---
> >>> fs/f2fs/segment.c | 5 ++++-
> >>> 1 file changed, 4 insertions(+), 1 deletion(-)
> >>>
> >>>diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>>index dced46c..df30220 100644
> >>>--- a/fs/f2fs/segment.c
> >>>+++ b/fs/f2fs/segment.c
> >>>@@ -1112,6 +1112,8 @@ static void __init_discard_policy(struct
> >>>f2fs_sb_info *sbi,
> >>> struct discard_policy *dpolicy,
> >>> int discard_type, unsigned int granularity)
> >>> {
> >>>+ struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> >>>+
> >>> /* common policy */
> >>> dpolicy->type = discard_type;
> >>> dpolicy->sync = true;
> >>>@@ -1129,7 +1131,8 @@ static void __init_discard_policy(struct
> >>>f2fs_sb_info *sbi,
> >>> dpolicy->io_aware = true;
> >>> dpolicy->sync = false;
> >>> dpolicy->ordered = true;
> >>>- if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL) {
> >>>+ if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL &&
> >>>+ atomic_read(&dcc->discard_cmd_cnt)) {
> >>> dpolicy->granularity = 1;
> >>> dpolicy->max_interval = DEF_MIN_DISCARD_ISSUE_TIME;
> >>> }
> >>>
> >
--
--
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
