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Fri, 11 Dec 2020 12:41:33 -0800 (PST) MIME-Version: 1.0 References: <20201211202140.396852-1-pasha.tatashin@soleen.com> <20201211202140.396852-6-pasha.tatashin@soleen.com> <20201211202354.GA2225686@ziepe.ca> In-Reply-To: <20201211202354.GA2225686@ziepe.ca> From: Pavel Tatashin Date: Fri, 11 Dec 2020 15:40:57 -0500 Message-ID: Subject: Re: [PATCH v3 5/6] mm/gup: migrate pinned pages out of movable zone To: Jason Gunthorpe Cc: LKML , linux-mm , Andrew Morton , Vlastimil Babka , Michal Hocko , David Hildenbrand , Oscar Salvador , Dan Williams , Sasha Levin , Tyler Hicks , Joonsoo Kim , mike.kravetz@oracle.com, Steven Rostedt , Ingo Molnar , Peter Zijlstra , Mel Gorman , Matthew Wilcox , David Rientjes , John Hubbard , Linux Doc Mailing List Content-Type: text/plain; charset="UTF-8" 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 Fri, Dec 11, 2020 at 3:23 PM Jason Gunthorpe wrote: > > On Fri, Dec 11, 2020 at 03:21:39PM -0500, Pavel Tatashin wrote: > > @@ -1593,7 +1592,7 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm, > > } > > > > if (!isolate_lru_page(head)) { > > - list_add_tail(&head->lru, &cma_page_list); > > + list_add_tail(&head->lru, &movable_page_list); > > mod_node_page_state(page_pgdat(head), > > NR_ISOLATED_ANON + > > page_is_file_lru(head), > > @@ -1605,7 +1604,7 @@ static long check_and_migrate_cma_pages(struct mm_struct *mm, > > i += step; > > } > > > > - if (!list_empty(&cma_page_list)) { > > + if (!list_empty(&movable_page_list)) { > > You didn't answer my earlier question, is it OK that ZONE_MOVABLE > pages leak out here if ioslate_lru_page() fails but the > moval_page_list is empty? > > I think the answer is no, right? In my opinion it is OK. We are doing our best to not pin movable pages, but if isolate_lru_page() fails because pages are currently locked by someone else, we will end up long-term pinning them. See comment in this patch: + * 1. Pinned pages: (long-term) pinning of movable pages is avoided + * when pages are pinned and faulted, but it is still possible that + * address space already has pages in ZONE_MOVABLE at the time when + * pages are pinned (i.e. user has touches that memory before + * pinning). In such case we try to migrate them to a different zone, + * but if migration fails the pages can still end-up pinned in + * ZONE_MOVABLE. In such case, memory offlining might retry a long + * time and will only succeed once user application unpins pages. > > Jason