Re: [PATCH] f2fs: fix is_idle() check for discard type

[Chao Yu]

On 2019/6/6 17:38, Sahitya Tummala wrote:
> The discard thread should issue upto dpolicy->max_requests at once
> and wait for all those discard requests at once it reaches
> dpolicy->max_requests. It should then sleep for dpolicy->min_interval
> timeout before issuing the next batch of discard requests. But in the
> current code of is_idle(), it checks for dcc_info->queued_discard and
> aborts issuing the discard batch of max_requests. This
> dcc_info->queued_discard will be true always once one discard command
> is issued.
> 
> It is thus resulting into this type of discard request pattern -
> 
> - Issue discard request#1
> - is_idle() returns false, discard thread waits for request#1 and then
>   sleeps for min_interval 50ms.
> - Issue discard request#2
> - is_idle() returns false, discard thread waits for request#2 and then
>   sleeps for min_interval 50ms.
> - and so on for all other discard requests, assuming f2fs is idle w.r.t
>   other conditions.
> 
> With this fix, the pattern will look like this -
> 
> - Issue discard request#1
> - Issue discard request#2
>   and so on upto max_requests of 8
> - Issue discard request#8
> - wait for min_interval 50ms.
> 

Fixes: fef4129ec2e6 ("f2fs: fix to be aware discard/preflush/dio command in
is_idle()")

> Signed-off-by: Sahitya Tummala <stummala@xxxxxxxxxxxxxx>

Ah, thanks for fixing this bug.

Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>

Thanks,