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Date: Tue, 16 Mar 2021 15:04:06 +0530
From: Sahitya Tummala <stummala@...eaurora.org>
To: Chao Yu <yuchao0@...wei.com>
Cc: Jaegeuk Kim <jaegeuk@...nel.org>,
linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org, stummala@...eaurora.org
Subject: Re: [PATCH] f2fs: fix the discard thread sleep timeout under high
utilization
Hi Chao,
Thanks for the review and suggestions.
I think the below code should work and cover all the cases we discussed.
Let me test it and then put up a new patchset for review.
Thanks,
Sahitya.
Mon, Mar 15, 2021 at 06:31:00PM +0800, Chao Yu wrote:
> Hi Sahitya,
>
> On 2021/3/15 17:45, Sahitya Tummala wrote:
> >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
>
> I think so.
>
> >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;
> >+ }
>
> Hmm.. how about cleaning up to configure discard policy in
> __init_discard_policy()?
>
> Something like:
>
> ---
> fs/f2fs/segment.c | 19 ++++++++++++-------
> 1 file changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 592927ccffa7..684463a70eb9 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1118,7 +1118,9 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi,
> dpolicy->ordered = true;
> if (utilization(sbi) > DEF_DISCARD_URGENT_UTIL) {
> dpolicy->granularity = 1;
> - dpolicy->max_interval = DEF_MIN_DISCARD_ISSUE_TIME;
> + if (atomic_read(&SM_I(sbi)->dcc_info->discard_cmd_cnt))
> + dpolicy->max_interval =
> + DEF_MIN_DISCARD_ISSUE_TIME;
> }
> } else if (discard_type == DPOLICY_FORCE) {
> dpolicy->min_interval = DEF_MIN_DISCARD_ISSUE_TIME;
> @@ -1734,8 +1736,15 @@ static int issue_discard_thread(void *data)
> set_freezable();
>
> do {
> - __init_discard_policy(sbi, &dpolicy, DPOLICY_BG,
> - dcc->discard_granularity);
> + if (sbi->gc_mode == GC_URGENT_HIGH ||
> + !f2fs_available_free_memory(sbi, DISCARD_CACHE))
> + __init_discard_policy(sbi, &dpolicy, DPOLICY_FORCE, 1);
> + else
> + __init_discard_policy(sbi, &dpolicy, DPOLICY_BG,
> + dcc->discard_granularity);
> +
> + if (!atomic_read(&dcc->discard_cmd_cnt))
> + wait_ms = dpolicy.max_interval;
>
> wait_event_interruptible_timeout(*q,
> kthread_should_stop() || freezing(current) ||
> @@ -1762,10 +1771,6 @@ static int issue_discard_thread(void *data)
> 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);
> -
> sb_start_intwrite(sbi->sb);
>
> issued = __issue_discard_cmd(sbi, &dpolicy);
> --
> 2.29.2
>
> Thoughts?
>
> Thanks,
>
> >+
> > sb_start_intwrite(sbi->sb);
> >
> > issued = __issue_discard_cmd(sbi, &dpolicy);
> >
> >thanks,
> >Sahitya.
> >
> >>Thanks,
> >>
> >>>
> >>>Thanks,
> >>>Sahitya.
> >>>
> >>>>Thanks,
> >>>>
> >>>>>
> >>>>>Signed-off-by: Sahitya Tummala <stummala@...eaurora.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.
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