On Wed 13-01-21 13:22:07, Muchun Song wrote: > There is a race between dissolve_free_huge_page() and put_page(). > Theoretically, we should return -EBUSY when we encounter this race. > In fact, we have a chance to successfully dissolve the page if we > do a retry. Because the race window is quite small. If we seize > this opportunity, it is an optimization for increasing the success > rate of dissolving page. > > Signed-off-by: Muchun Song <[email protected]> > --- > mm/hugetlb.c | 20 ++++++++++++++++++-- > 1 file changed, 18 insertions(+), 2 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 4a9011e12175..898e4ea43e13 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1772,6 +1772,7 @@ int dissolve_free_huge_page(struct page *page) > { > int rc = -EBUSY; > > +retry: > /* Not to disrupt normal path by vainly holding hugetlb_lock */ > if (!PageHuge(page)) > return 0; > @@ -1793,8 +1794,23 @@ int dissolve_free_huge_page(struct page *page) > * We should make sure that the page is already on the free list > * when it is dissolved. > */ > - if (unlikely(!PageHugeFreed(head))) > - goto out; > + if (unlikely(!PageHugeFreed(head))) { > + spin_unlock(&hugetlb_lock); > + > + /* > + * Theoretically, we should return -EBUSY when we > + * encounter this race. In fact, we have a chance > + * to successfully dissolve the page if we do a > + * retry. Because the race window is quite small. > + * If we seize this opportunity, it is an optimization > + * for increasing the success rate of dissolving page. > + */ > + while (PageHeadHuge(head) && !PageHugeFreed(head)) { > + cond_resched(); > + cpu_relax(); > + } > + goto retry;
OK, so you have done the retry here. Please fold it into the previous patch. Also do we need cpu_relax on top of cond_resched as well? > + } > > /* > * Move PageHWPoison flag from head page to the raw error page, > -- > 2.11.0 -- Michal Hocko SUSE Labs
