On Thu, 10 Oct 2019 15:17:47 -0400 Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> 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.
> */
This?
--- a/mm/page_io.c~mm-annotate-refault-stalls-from-swap_readpage-fix
+++ a/mm/page_io.c
@@ -361,6 +361,11 @@ int swap_readpage(struct page *page, boo
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(PageUptodate(page), page);
+ /*
+ * 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.
+ */
psi_memstall_enter(&pflags);
if (frontswap_load(page) == 0) {
_
