Re: [PATCH 4/7] migrate_pages(): fix failure counting for THP subpages retrying

[Baolin Wang]

On 6/27/2022 9:46 AM, Huang, Ying wrote:
> Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:
>
> > On 6/24/2022 10:53 AM, Huang Ying wrote:
> > > If THP is failed to be migrated for -ENOSYS and -ENOMEM, the THP will
> > > be split into thp_split_pages, and after other pages are migrated,
> > > pages in thp_split_pages will be migrated with no_subpage_counting ==
> > > true, because its failure have been counted already.  If some pages in
> > > thp_split_pages are retried during migration, we should not count
> > > their failure if no_subpage_counting == true too.  This is done this
> > > patch to fix the failure counting for THP subpages retrying.
> >
> > Good catch. Totally agree with you. It seems we can move the condition
> > into -EAGAIN case like other cases did?
> >
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index 1ece23d80bc4..491c2d07402b 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -1463,7 +1463,7 @@ int migrate_pages(struct list_head *from,
> > new_page_t get_new_page,
> >                          case -EAGAIN:
> >                                  if (is_thp)
> >                                          thp_retry++;
> > -                               else
> > +                               else if (!no_subpage_counting)
> >                                          retry++;
> >                                  break;
>
> This has another effect except fixing the failure counting.  That is,
> the split subpages of THP will not be retried for 10 times for -EAGAIN.

Ah, yes.

> TBH, I think that we should do that.  But because this has some behavior

OK. So you afraid that 10 times retry for each subpage of THP will waste 
lots of time?

> change, it's better to be done in a separate patch?  Do you have
> interest to do that on top of this patchset?

Sure. I can send a patch which can be folded into your series. Is this 
OK for you?

By the way, if I do like I said, the patch 4 can be avoided.

> > Anyway this patch looks good to me.
> > Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>
> Thanks!
>
> Best Regards,
> Huang, Ying
>
> > > Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> > > Fixes: 5984fabb6e82 ("mm: move_pages: report the number of non-attempted pages")
> > > Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > > Cc: Zi Yan <ziy@xxxxxxxxxx>
> > > Cc: Yang Shi <shy828301@xxxxxxxxx>
> > > --- >   mm/migrate.c | 3 ++-
> > >    1 file changed, 2 insertions(+), 1 deletion(-)
> > > diff --git a/mm/migrate.c b/mm/migrate.c
> > > index 542533e4e3cf..61dab3025a1d 100644
> > > --- a/mm/migrate.c
> > > +++ b/mm/migrate.c
> > > @@ -1477,7 +1477,8 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
> > >    			}
> > >    		}
> > >    	}
> > > -	nr_failed += retry;
> > > +	if (!no_subpage_counting)
> > > +		nr_failed += retry;
> > >    	nr_thp_failed += thp_retry;
> > >    	/*
> > >    	 * Try to migrate subpages of fail-to-migrate THPs, no nr_failed