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[2003:cb:c723:4c00:5c85:5575:c321:cea3]) by smtp.gmail.com with ESMTPSA id x1-20020a5d54c1000000b003176f2d9ce5sm13606935wrv.71.2023.07.31.09.20.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 31 Jul 2023 09:20:09 -0700 (PDT) Message-ID: Date: Mon, 31 Jul 2023 18:20:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v1 0/4] smaps / mm/gup: fix gup_can_follow_protnone fallout To: Peter Xu Cc: Linus Torvalds , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Andrew Morton , liubo , Matthew Wilcox , Hugh Dickins , Jason Gunthorpe , John Hubbard , Mel Gorman References: <20230727212845.135673-1-david@redhat.com> <412bb30f-0417-802c-3fc4-a4e9d5891c5d@redhat.com> <66e26ad5-982e-fe2a-e4cd-de0e552da0ca@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; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 9644540012 X-Stat-Signature: dexk4nztzt1kubird1tg1adrkwn8mm4p X-HE-Tag: 1690820414-116523 X-HE-Meta: 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 3Q/Isy31 cwG819zwW+7CVsa8ZF6c7QYJuPTSOJRfKVMWd4Ks/XY2fuwgCdETUz63yxsCLAv9t8EFHqsmYeSuxFjq+QxL+zN6wuLN6Y9T4/5LyBDmqeyvsrt6g2Jn78+3evMSWasoU5yQ0zhVxUp1lKNL3fH3NK8BlSOfPUFkEOr0MSO9o4idHS/b1FzBuMTkLGHYqcisoDSNK21D52j+m6Xji1VVHrtLmME4jvuSGkNEZyEvLroXQZwlt0Hw4pgsZyn4f9FS56vmgkweaZTd5Pi6ZqWZSGB5TsaMxBxPGCeNJ12EQPRf2SkahoNHbDfaXCTNvKSiYKwvPl2BtEUuKva4u8XgKyW07x5a2LyOH+5L/LCkDEiwMXxyGy/GoFLDebzbvXI7YG8ujA2Y0etYlnfBDMGNWsIjpv2536eF61FUpzjwfIkQRRk4eOTJob+ksgA== 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: >> (2) Consequently, commit c46a7c817e66 from 2014 does not tell the whole >> story. >> >> commit 21d9ee3eda77 ("mm: remove remaining references to NUMA >> hinting bits and helpers") from 2015 made the distinction again >> impossible. >> >> Setting FOLL_FORCE | FOLL_HONOR_NUMA_HINT would end up never making >> progress in GUP with an inaccessible (PROT_NONE) VMA. > > If we also teach follow_page_mask() on vma_is_accessible(), we should still > be good, am I right? > > Basically fast-gup will stop working on protnone, and it always fallbacks > to slow-gup. Then it seems we're good decoupling FORCE with NUMA hint. > > I assume that that's what you did below in the patch too, which looks right > to me. I modified it slightly: FOLL_HONOR_NUMA_FAULT is now set in is_valid_gup_args(), such that it will always be set for any GUP users, including GUP-fast. [...] >> +/* >> + * Indicates whether GUP can follow a PROT_NONE mapped page, or whether >> + * a (NUMA hinting) fault is required. >> + */ >> +static inline bool gup_can_follow_protnone(struct vm_area_struct *vma, >> + unsigned int flags) >> +{ >> + /* >> + * If callers don't want to honor NUMA hinting faults, no need to >> + * determine if we would actually have to trigger a NUMA hinting fault. >> + */ >> + if (!(flags & FOLL_HONOR_NUMA_FAULT)) >> + return true; >> + >> + /* We really need the VMA ... */ >> + if (!vma) >> + return false; > > I'm not sure whether the compiler will be smart enough to inline this for > fast-gup on pmd/pte. Why shouldn't it? It's placed in a head file and the vma == NULL is not obfuscated. :) Anyhow, I'll take a look at the compiler output. Thanks! -- Cheers, David / dhildenb