On 8/11/20 4:19 PM, Wei Yang wrote: > On Tue, Aug 11, 2020 at 02:43:28PM -0700, Mike Kravetz wrote: >> Subject: [PATCH] hugetlb: optimize race error return in >> alloc_surplus_huge_page >> >> The routine alloc_surplus_huge_page() could race with with a pool >> size change. If this happens, the allocated page may not be needed. >> To free the page, the current code will 'Abuse temporary page to >> workaround the nasty free_huge_page codeflow'. Instead, directly >> call the low level routine that free_huge_page uses. This works >> out well because the page is new, we hold the only reference and >> already hold the hugetlb_lock. >> >> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> >> --- >> mm/hugetlb.c | 13 ++++++++----- >> 1 file changed, 8 insertions(+), 5 deletions(-) >> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index 590111ea6975..ac89b91fba86 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -1923,14 +1923,17 @@ static struct page *alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask, >> /* >> * We could have raced with the pool size change. >> * Double check that and simply deallocate the new page >> - * if we would end up overcommiting the surpluses. Abuse >> - * temporary page to workaround the nasty free_huge_page >> - * codeflow >> + * if we would end up overcommiting the surpluses. >> */ >> if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages) { >> - SetPageHugeTemporary(page); >> + /* >> + * Since this page is new, we hold the only reference, and >> + * we already hold the hugetlb_lock call the low level free >> + * page routine. This saves at least a lock roundtrip. > > The change looks good to me, while I may not understand the "lock roundtrip". > You mean we don't need to release the hugetlb_lock? Correct. Normally we would free the page via free_huge_page() processing. To do that we need to drop hugetlb_lock and call put_page/free_huge_page which will need to acquire the hugetlb_lock again. -- Mike Kravetz > >> + */ >> + (void)put_page_testzero(page); /* don't call destructor */ >> + update_and_free_page(h, page); >> spin_unlock(&hugetlb_lock); >> - put_page(page); >> return NULL; >> } else { >> h->surplus_huge_pages++; >> -- >> 2.25.4