Messages in this thread | | | From | "Huang, Ying" <> | Subject | Re: [PATCH 1/2] mm: gup: Re-pin pages in case of trying several times to migrate | Date | Thu, 20 Oct 2022 16:15:16 +0800 |
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Baolin Wang <baolin.wang@linux.alibaba.com> writes:
> The migrate_pages() will return the number of {normal page, THP, hugetlb} > that were not migrated, or an error code. That means it can still return > the number of failure count, though the pages have been migrated > successfully with several times re-try.
If my understanding were correct, if pages are migrated successfully after several times re-tries, the return value will be 0. There's one possibility for migrate_pages() to return non-zero but all pages are migrated. That is, when THP is split and all subpages are migrated successfully.
> So we should not use the return value of migrate_pages() to determin > if there are pages are failed to migrate. Instead we can validate the > 'movable_page_list' to see if there are pages remained in the list, > which are failed to migrate. That can mitigate the failure of longterm > pinning.
Another choice is to use a special return value for split THP + success migration. But I'm fine to use list_empty(return_pages).
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> > --- > mm/gup.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index 5182aba..bd8cfcd 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -1914,9 +1914,10 @@ static int migrate_longterm_unpinnable_pages( > .gfp_mask = GFP_USER | __GFP_NOWARN, > }; > > - if (migrate_pages(movable_page_list, alloc_migration_target, > - NULL, (unsigned long)&mtc, MIGRATE_SYNC, > - MR_LONGTERM_PIN, NULL)) { > + ret = migrate_pages(movable_page_list, alloc_migration_target, > + NULL, (unsigned long)&mtc, MIGRATE_SYNC, > + MR_LONGTERM_PIN, NULL); > + if (ret < 0 || !list_empty(movable_page_list)) {
It seems that !list_empty() is sufficient here.
> ret = -ENOMEM;
Why change the error code? I don't think it's a good idea to do that.
> goto err; > }
Best Regards, Huang, Ying
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