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Sat, 07 May 2022 17:28:54 -0700 (PDT) X-Google-Smtp-Source: ABdhPJyWPkh3zBSc9oc61q1WzL0NdJ1Avcf+UZ74YgB60XC3dfGeDmiVRDE4qcyYoknIHnJJK5aBVQ== X-Received: by 2002:a0c:cc08:0:b0:45a:8f81:d8a8 with SMTP id r8-20020a0ccc08000000b0045a8f81d8a8mr8527257qvk.88.1651969733946; Sat, 07 May 2022 17:28:53 -0700 (PDT) Received: from [10.23.153.165] ([46.248.132.196]) by smtp.gmail.com with ESMTPSA id c2-20020ac80542000000b002f39b99f67bsm4852527qth.21.2022.05.07.17.28.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 07 May 2022 17:28:53 -0700 (PDT) Message-ID: Date: Sun, 8 May 2022 02:28:51 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH] mm: fix is_pinnable_page against on cma page To: Minchan Kim Cc: Andrew Morton , linux-mm , LKML , John Hubbard , John Dias References: <20220502173558.2510641-1-minchan@kernel.org> <29d0c1c3-a44e-4573-7e7e-32be07544dbe@redhat.com> <08e9855c-395d-f40c-de3d-1ec8b644bfe8@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 80540180005 X-Stat-Signature: oucdwtxozwtnrci9g1tqh7g3j35w1a9n Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=RWkhOkfF; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf06.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1651969734-182342 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 05.05.22 08:48, Minchan Kim wrote: > On Wed, May 04, 2022 at 03:48:54PM -0700, Minchan Kim wrote: >> On Tue, May 03, 2022 at 06:02:33PM +0200, David Hildenbrand wrote: >>> On 03.05.22 17:26, Minchan Kim wrote: >>>> On Tue, May 03, 2022 at 03:15:24AM +0200, David Hildenbrand wrote: >>>>> >>>>>>>>> However, I assume we have the same issue right now already with >>>>>>> ZONE_MOVABLE and MIGRATE_CMA when trying to pin a page residing on these >>>>>> >>>>>> ZONE_MOVALBE is also changed dynamically? >>>>>> >>>>> >>>>> Sorry, with "same issue" I meant failing to pin if having to migrate and >>>>> the page is temporarily unmovable. >>>>> >>>>>>> there are temporarily unmovable and we fail to migrate. But it would now >>>>>>> apply even without ZONE_MOVABLE or MIGRATE_CMA. Hm... >>>>>> >>>>>> Didn't parse your last mention. >>>>> >>>>> On a system that neither uses ZONE_MOVABLE nor MIGRATE_CMA we might have >>>>> to migrate now when pinning. >>>> >>>> I don't understand your point. My problem is pin_user_pages with >>>> FOLL_LONGTERM. It shouldn't pin a page from ZONE_MOVABLE and cma area >>>> without migrating page out of movable zone or CMA area. >>>> That's why try_grab_folio checks whether target page stays in those >>>> movable areas. However, to check CMA area, is_migrate_cma_page is >>>> racy so the FOLL_LONGTERM flag semantic is broken right now. >>>> >>>> Do you see any problem of the fix? >>> >>> My point is that you might decide to migrate a page because you stumble >>> over MIGRATE_ISOLATE, although there is no need to reject long-term >>> pinning and to trigger page migration. >>> >>> Assume a system without ZONE_MOVABLE and without MIGRATE_CMA. Assume >>> someone reserves gigantic pages (alloc_contig_range()) and you have >>> concurrent long-term pinning on a page that is no MIGRATE_ISOLATE. >>> >>> GUP would see MIGRATE_ISOLATE and would reject pinning. The page has to >>> be migrated, which can fail if the page is temporarily unmovable. >> >> A dump question since I'm not familiar with hugetlb. >> >> Is above reasonable scenario? >> >> The gigantic page is about to be created using alloc_contig_range so >> they has MIGRATE_ISOLATE as temporal state. It means no one uses the >> page yet so I guess the page is not mapped at userspace but other is >> trying to access the page using pin_user_pages? >> > > Too dump question. Never mind. > Posted v2 - https://lore.kernel.org/all/20220505064429.2818496-1-minchan@kernel.org/T/#u Sorry for the late reply, still traveling :) Just so we're on the same page: MIGRATE_ISOLATE would be set on pageblocks that contain either free or movable pages. In case of movable pages, they are in uese. Regarding your is_cma_page() proposal, I think we might want to consider that if it really turns out to be a problem. For now, I'm fine with just documenting it. Thanks! -- Thanks, David / dhildenb