Re: [PATCH] mm : bail out from psi memstall after submit_bio in swap_readpage

[Zhaoyang Huang]

On Tue, Sep 7, 2021 at 8:03 PM Vlastimil Babka <vbabka@xxxxxxx> wrote:
>
> On 9/7/21 13:59, Huangzhaoyang wrote:
> > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> >
> > It doesn't make sense to count IO time into psi memstall. Bail out after
> > bio submitted.
>
> Isn't that the point if psi, to observe real stalls, which include IO?
> Anyway, CCing Johannes.
IO stalls could be observed within blk_io_schedule. The time cost of
the data from block device to RAM is counted here. The original
purpose is to deal with the ZRAM alike devices which deal with the bio
locally instead of submitting it to request queue.
>
> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> > ---
> >  mm/page_io.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/page_io.c b/mm/page_io.c
> > index c493ce9..1d131fc 100644
> > --- a/mm/page_io.c
> > +++ b/mm/page_io.c
> > @@ -423,6 +423,7 @@ int swap_readpage(struct page *page, bool synchronous)
> >       count_vm_event(PSWPIN);
> >       bio_get(bio);
> >       qc = submit_bio(bio);
> > +     psi_memstall_leave(&pflags);
> >       while (synchronous) {
> >               set_current_state(TASK_UNINTERRUPTIBLE);
> >               if (!READ_ONCE(bio->bi_private))
> > @@ -433,7 +434,7 @@ int swap_readpage(struct page *page, bool synchronous)
> >       }
> >       __set_current_state(TASK_RUNNING);
> >       bio_put(bio);
> > -
> > +     return ret;
> >  out:
> >       psi_memstall_leave(&pflags);
> >       return ret;
> >
>