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spf=pass (imf07.hostedemail.com: domain of mike.kravetz@oracle.com designates 205.220.165.32 as permitted sender) smtp.mailfrom=mike.kravetz@oracle.com; dmarc=pass (policy=none) header.from=oracle.com; arc=pass ("microsoft.com:s=arcselector9901:i=1") X-Stat-Signature: a318c8y6axtnnbqwdq8q9w7z6wf346ew X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0690440164 Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=oracle.com header.s=corp-2022-7-12 header.b=QxdLE693; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=Et4zebdb; spf=pass (imf07.hostedemail.com: domain of mike.kravetz@oracle.com designates 205.220.165.32 as permitted sender) smtp.mailfrom=mike.kravetz@oracle.com; dmarc=pass (policy=none) header.from=oracle.com; arc=pass ("microsoft.com:s=arcselector9901:i=1") X-HE-Tag: 1660063048-535784 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 08/09/22 10:48, Miaohe Lin wrote: > On 2022/8/9 5:28, Mike Kravetz wrote: > > There have been proposals to change at least the buddy allocator to > > return frozen pages as described at [3]. If such a change is made, it > > can be employed by the hugetlb code. However, as mentioned above > > hugetlb uses several low level allocators so each would need to be > > modified to return frozen pages. For now, we can manually freeze the > > returned pages. This is done in two places: > > 1) alloc_buddy_huge_page, only the returned head page is ref counted. > > We freeze the head page, retrying once in the VERY rare case where > > there may be an inflated ref count. > > 2) prep_compound_gigantic_page, for gigantic pages the current code > > freezes all pages except the head page. New code will simply freeze > > the head page as well. > > > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > > index 28516881a1b2..6b90d85d545b 100644 > > --- a/mm/hugetlb.c > > +++ b/mm/hugetlb.c > > @@ -1769,13 +1769,12 @@ static bool __prep_compound_gigantic_page(struct page *page, unsigned int order, > > { > > int i, j; > > int nr_pages = 1 << order; > > - struct page *p = page + 1; > > + struct page *p = page; > > > > /* we rely on prep_new_huge_page to set the destructor */ > > set_compound_order(page, order); > > - __ClearPageReserved(page); > > __SetPageHead(page); > > - for (i = 1; i < nr_pages; i++, p = mem_map_next(p, page, i)) { > > + for (i = 0; i < nr_pages; i++, p = mem_map_next(p, page, i)) { > > /* > > * For gigantic hugepages allocated through bootmem at > > * boot, it's safer to be consistent with the not-gigantic > > @@ -1814,7 +1813,8 @@ static bool __prep_compound_gigantic_page(struct page *page, unsigned int order, > > } else { > > VM_BUG_ON_PAGE(page_count(p), p); > > } > > - set_compound_head(p, page); > > + if (i != 0) > > + set_compound_head(p, page); > > It seems we forget to unfreeze the head page in out_error path. If unexpected inflated ref count occurs, > the ref count of head page will become negative in free_gigantic_page? Yes, thank you! I forgot to modify the error path to also fix up the head page. -- Mike Kravetz