Re: [External] Re: [PATCH v2 4/6] mm: hugetlb: add return -EAGAIN for dissolve_free_huge_page

[Muchun Song]

On Thu, Jan 7, 2021 at 1:07 AM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Wed 06-01-21 16:47:37, Muchun Song wrote:
> > When dissolve_free_huge_page() races with __free_huge_page(), we can
> > do a retry. Because the race window is small.
>
> Is this a bug fix or mere optimization. I have hard time to tell from
> the description.

It is optimization. Thanks.

>
> > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> > ---
> >  mm/hugetlb.c | 26 +++++++++++++++++++++-----
> >  1 file changed, 21 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> [...]
> > @@ -1825,6 +1828,14 @@ int dissolve_free_huge_page(struct page *page)
> >       }
> >  out:
> >       spin_unlock(&hugetlb_lock);
> > +
> > +     /*
> > +      * If the freeing of the HugeTLB page is put on a work queue, we should
> > +      * flush the work before retrying.
> > +      */
> > +     if (unlikely(rc == -EAGAIN))
> > +             flush_work(&free_hpage_work);
>
> Is it safe to wait for the work to finish from this context?

Yes. It is safe.

>
> --
> Michal Hocko
> SUSE Labs