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.
So, to avoid this case, shouldn't we reset wait_ms to dpolicy.max_interval
at [1]?
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?
Thanks,
>
> Thanks,
> Sahitya.
>
>> Thanks,
>>
>>>
>>> Signed-off-by: Sahitya Tummala <[email protected]>
>>> ---
>>> 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;
>>> }
>>>
>