On 2018/12/19 6:43, Jaegeuk Kim wrote:
> On 12/18, Chao Yu wrote:
>> On 2018/12/14 13:01, Jaegeuk Kim wrote:
>>> Sometimes, I could observe # of issuing_discard to be 1 which blocks
>>> background
>>> jobs due to is_idle()=false.
>>> The only way to get out of it was to trigger gc_urgent. This patch avoids
>>> that
>>> by checking any candidates as done in the list.
>>
>> Well, as below code, once we issued discard commands, we will wait all
>> queued discard end their IO, so do you know what flow can cause such
>> condition...?
>
> It's very subtle, and I suspect somehow race condition not from here.
>
>>
>> issued = __issue_discard_cmd(sbi, &dpolicy);
>> if (issued > 0) {
>> __wait_all_discard_cmd(sbi, &dpolicy);
>>
>> Or, I doubt that 'issued' statistical info could be wrong.
>
> No, it simply came back to 0 with this patch. So, something is pending
> in the queue even if it is done.
__submit_discard_cmd()
{
....
dc->len = 0; <---- reset discard length here
while (total_len && *issued < dpolicy->max_requests && !err) {
struct bio *bio = NULL;
unsigned long flags;
bool last = true;
if (len > max_discard_blocks) {
len = max_discard_blocks; <---- will truncate len to
max_discard_blocks
last = false;
}
(*issued)++;
if (*issued == dpolicy->max_requests)
last = true;
dc->len += len; <----- will update len into dc->len
...
}
__wait_discard_cmd_range()
{
...
if (dc->len < dpolicy->granularity)
continue;
So we can only remove discard entry which size is not smaller than
dpolicy->granularity, if max_discard_blocks is smaller than granularity,
after splitting discard in __submit_discard_cmd(), we may left small-sized
entry there.
...
}
Could you check that whether the left discard was skipped being removed due
to above reason?
Thanks
>
> Thanks,
>
>>
>> Thanks,
>>
>>>
>>> Signed-off-by: Jaegeuk Kim <jaeg...@kernel.org>
>>> ---
>>> fs/f2fs/segment.c | 4 ++++
>>> 1 file changed, 4 insertions(+)
>>>
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index 49ea9009ab5a..acbbc924e518 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -1651,6 +1651,10 @@ static int issue_discard_thread(void *data)
>>> if (dcc->discard_wake)
>>> dcc->discard_wake = 0;
>>>
>>> + /* clean up pending candidates before going to sleep */
>>> + if (atomic_read(&dcc->queued_discard))
>>> + __wait_all_discard_cmd(sbi, NULL);
>>> +
>>> if (try_to_freeze())
>>> continue;
>>> if (f2fs_readonly(sbi->sb))
>>>
>
> .
>
