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[2003:cb:c706:8900:2c18:b992:1fa1:f88b]) by smtp.gmail.com with ESMTPSA id c16-20020adffb50000000b002205c907474sm226711wrs.107.2022.08.04.00.40.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 04 Aug 2022 00:40:33 -0700 (PDT) Message-ID: <4cfb6fd5-f820-b56d-bbfe-13c92a5bf682@redhat.com> Date: Thu, 4 Aug 2022 09:40:33 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v2] mm/gup.c: Simplify and fix check_and_migrate_movable_pages() return codes To: Alistair Popple , Andrew Morton Cc: linux-mm@kvack.org, jgg@nvidia.com, minchan@kernel.org, linux-kernel@vger.kernel.org, jhubbard@nvidia.com, pasha.tatashin@soleen.com References: <814dee5d3aadd38c3370eaaf438ba7eee9bf9d2b.1659399696.git-series.apopple@nvidia.com> <20220802171215.3c909e1984ec345ff94af155@linux-foundation.org> <87czdg7tlt.fsf@nvdebian.thelocal> From: David Hildenbrand Organization: Red Hat In-Reply-To: <87czdg7tlt.fsf@nvdebian.thelocal> 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 ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1659598837; a=rsa-sha256; cv=none; b=SdyILPfidRuDlUcQmEFBjaLHJr1LRMZi3tgBepKvAEjmNryEBQlj+Ooq+toU1CCSkxvDJO HjL7tSBW0M9cZgwIVPbVYIU2qF4nzdKLNsm2jDE5m7Z466ZxUJGnfpYeXnZxXbEbV8qCuz Nzt0Z+x2JTAGpRCZiHsRCOSAJ2tyTTc= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Vxs+fw2c; spf=pass (imf18.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1659598837; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=+WZV3/cdkw6cQVZQcHjV7n6CKEOnJ0svsTCr3g/sk6M=; b=VB845gFOMX5bKW3k3NkMl5zSJR9z7z8twbItQ7Ocsril+3CnzA92oU8+mmzZ81I99Ix644 dnlA7bl3XPOlX3RFeGv1R7fBDqtCnvIUggU7qeLBzahU4xYBWoOK/uL9eISPvfrva4zS7v UqDe5Nwp3aFjmAoqN55sp2BC4pGJ84I= X-Stat-Signature: 7ycs5sgrcwa13abr54z1u11r3s6usgew X-Rspamd-Queue-Id: 3F03D1C0053 Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=Vxs+fw2c; spf=pass (imf18.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1659598837-438923 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 04.08.22 02:12, Alistair Popple wrote: > > Andrew Morton writes: > >> On Tue, 2 Aug 2022 10:30:12 +1000 Alistair Popple wrote: >> >>> When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() >>> is called to migrate pages out of zones which should not contain any >>> longterm pinned pages. >>> >>> When migration succeeds all pages will have been unpinned so pinning >>> needs to be retried. This is indicated by returning zero. When all pages >>> are in the correct zone the number of pinned pages is returned. >>> >>> However migration can also fail, in which case pages are unpinned and >>> -ENOMEM is returned. However if the failure was due to not being unable >>> to isolate a page zero is returned. This leads to indefinite looping in >>> __gup_longterm_locked(). >>> >>> Fix this by simplifying the return codes such that zero indicates all >>> pages were successfully pinned in the correct zone while errors indicate >>> either pages were migrated and pinning should be retried or that >>> migration has failed and therefore the pinning operation should fail. >>> >>> This fixes the indefinite looping on page isolation failure by failing >>> the pin operation instead of retrying indefinitely. >>> >> >> Are we able to identify a Fixes: for this? Presumably something in the >> series "Add MEMORY_DEVICE_COHERENT for coherent device memory mapping"? > > It seems the infinite loop was desired behaviour so I will re-spin this > as a pure clean-up. > How can the infinite loop trigger when we allow longterm-pinning the shared zeropage? (note: disallowing that for now was a bug) -- Thanks, David / dhildenb