Re: [PATCH] mm: annotate refault stalls from swap_readpage

From: Johannes Weiner
Date: Thu Oct 10 2019 - 15:17:51 EST

On Thu, Oct 10, 2019 at 08:21:34AM -0700, Minchan Kim wrote:
> From: Minchan Kim <minchan@xxxxxxxxxx>
> If block device supports rw_page operation, it doesn't submit bio
> so annotation in submit_bio for refault stall doesn't work.
> It happens with zram in android, especially swap read path which
> could consume CPU cycle for decompress. It is also a problem for
> zswap which uses frontswap.
> Annotate swap_readpage() to account the synchronous IO overhead
> to prevent underreport memory pressure.
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Can you please add a comment to the caller? Lifted from submit_bio():

* Count submission time as memory stall. When the device is
* congested, or the submitting cgroup IO-throttled,
* submission can be a significant part of overall IO time.