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Fri, 10 Apr 2026 15:27:44 +0000 (UTC) X-Farcaster-Flow-ID: 675e78a9-fd73-4b67-b9dc-b2724822a679 Received: from EX19D027UEC003.ant.amazon.com (10.252.137.250) by EX19MTAUEC002.ant.amazon.com (10.252.135.253) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.37; Fri, 10 Apr 2026 15:27:43 +0000 Received: from [192.168.12.97] (10.106.82.30) by EX19D027UEC003.ant.amazon.com (10.252.137.250) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.37; Fri, 10 Apr 2026 15:27:31 +0000 Message-ID: <28ecd1c9-184a-4514-b91f-e57944861641@amazon.com> Date: Fri, 10 Apr 2026 16:27:28 +0100 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [PATCH v11 05/16] mm/gup: drop local variable in gup_fast_folio_allowed To: Ackerley Tng , "David Hildenbrand (Arm)" , "Kalyazin, Nikita" , "kvm@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.linux.dev" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "bpf@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "kernel@xen0n.name" , "linux-riscv@lists.infradead.org" , "linux-s390@vger.kernel.org" , "loongarch@lists.linux.dev" , "linux-pm@vger.kernel.org" CC: "pbonzini@redhat.com" , "corbet@lwn.net" , "maz@kernel.org" , "oupton@kernel.org" , "joey.gouly@arm.com" , "suzuki.poulose@arm.com" , "yuzenghui@huawei.com" , "catalin.marinas@arm.com" , "will@kernel.org" , "seanjc@google.com" , "tglx@kernel.org" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "x86@kernel.org" , "hpa@zytor.com" , "luto@kernel.org" , "peterz@infradead.org" , "willy@infradead.org" , "akpm@linux-foundation.org" , "lorenzo.stoakes@oracle.com" , "vbabka@kernel.org" , "rppt@kernel.org" , "surenb@google.com" , "mhocko@suse.com" , "ast@kernel.org" , "daniel@iogearbox.net" , "andrii@kernel.org" , "martin.lau@linux.dev" , "eddyz87@gmail.com" , "song@kernel.org" , "yonghong.song@linux.dev" , "john.fastabend@gmail.com" , "kpsingh@kernel.org" , "sdf@fomichev.me" , "haoluo@google.com" , "jolsa@kernel.org" , "jgg@ziepe.ca" , "jhubbard@nvidia.com" , "peterx@redhat.com" , "jannh@google.com" , "pfalcato@suse.de" , "skhan@linuxfoundation.org" , "riel@surriel.com" , "ryan.roberts@arm.com" , "jgross@suse.com" , "yu-cheng.yu@intel.com" , "kas@kernel.org" , "coxu@redhat.com" , "kevin.brodsky@arm.com" , "yosry@kernel.org" , "ajones@ventanamicro.com" , "maobibo@loongson.cn" , "tabba@google.com" , "prsampat@amd.com" , "wu.fei9@sanechips.com.cn" , "mlevitsk@redhat.com" , "jmattson@google.com" , "jthoughton@google.com" , "agordeev@linux.ibm.com" , "alex@ghiti.fr" , "aou@eecs.berkeley.edu" , "borntraeger@linux.ibm.com" , "chenhuacai@kernel.org" , "dev.jain@arm.com" , "gor@linux.ibm.com" , "hca@linux.ibm.com" , "palmer@dabbelt.com" , "pjw@kernel.org" , "shijie@os.amperecomputing.com" , "svens@linux.ibm.com" , "thuth@redhat.com" , "wyihan@google.com" , "yang@os.amperecomputing.com" , "Jonathan.Cameron@huawei.com" , "Liam.Howlett@oracle.com" , "urezki@gmail.com" , "zhengqi.arch@bytedance.com" , "gerald.schaefer@linux.ibm.com" , "jiayuan.chen@shopee.com" , "lenb@kernel.org" , "osalvador@suse.de" , "pavel@kernel.org" , "rafael@kernel.org" , "vannapurve@google.com" , "jackmanb@google.com" , "aneesh.kumar@kernel.org" , "patrick.roy@linux.dev" , "Thomson, Jack" , "Itazuri, Takahiro" , "Manwaring, Derek" References: <20260317141031.514-1-kalyazin@amazon.com> <20260317141031.514-6-kalyazin@amazon.com> <0a14c10d-0dab-4b9c-85ec-e0ee25cd0db8@kernel.org> Content-Language: en-US From: Nikita Kalyazin Autocrypt: addr=kalyazin@amazon.com; keydata= xjMEY+ZIvRYJKwYBBAHaRw8BAQdA9FwYskD/5BFmiiTgktstviS9svHeszG2JfIkUqjxf+/N JU5pa2l0YSBLYWx5YXppbiA8a2FseWF6aW5AYW1hem9uLmNvbT7CjwQTFggANxYhBGhhGDEy BjLQwD9FsK+SyiCpmmTzBQJp2NfjBQkGQlIzAhsDBAsJCAcFFQgJCgsFFgIDAQAACgkQr5LK IKmaZPPNDAEAvsw8vEWj8ArWQ1QJNufjrvobU/cE8MLKdBxbSE8CyZQA/0BldKxNAtAwG4qw wCLxsZ5vBL3Zkh/PdvtFCj/VGscGzjgEY+ZIvRIKKwYBBAGXVQEFAQEHQCqd7/nb2tb36vZt ubg1iBLCSDctMlKHsQTp7wCnEc4RAwEIB8J+BBgWCAAmFiEEaGEYMTIGMtDAP0Wwr5LKIKma ZPMFAmnY1+MFCQZCUjMCGwwACgkQr5LKIKmaZPPQKgD/f3FtERbJ+LYHLSG/ZbLNAOLngUlQ qo5VfIyJOzeLzC0BAP2PIUFIHo7vmia/PXEmT+ve4c5rx+EkH/Dx1GRpjWoI In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: EX19D004EUA003.ant.amazon.com (10.252.50.230) To EX19D027UEC003.ant.amazon.com (10.252.137.250) On 23/03/2026 20:22, Ackerley Tng wrote: > "David Hildenbrand (Arm)" writes: > >> On 3/17/26 15:11, Kalyazin, Nikita wrote: >>> From: Nikita Kalyazin >>> >>> Move the check for pinning closer to where the result is used. >>> No functional changes. >>> >>> Signed-off-by: Nikita Kalyazin >>> --- >>> mm/gup.c | 23 ++++++++++++----------- >>> 1 file changed, 12 insertions(+), 11 deletions(-) >>> >>> diff --git a/mm/gup.c b/mm/gup.c >>> index 5856d35be385..869d79c8daa4 100644 >>> --- a/mm/gup.c >>> +++ b/mm/gup.c >>> @@ -2737,18 +2737,9 @@ EXPORT_SYMBOL(get_user_pages_unlocked); >>> */ >>> static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags) >>> { >>> - bool reject_file_backed = false; >>> struct address_space *mapping; >>> unsigned long mapping_flags; >>> >>> - /* >>> - * If we aren't pinning then no problematic write can occur. A long term >>> - * pin is the most egregious case so this is the one we disallow. >>> - */ >>> - if ((flags & (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE)) == >>> - (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE)) >>> - reject_file_backed = true; >>> - >>> /* We hold a folio reference, so we can safely access folio fields. */ >>> if (WARN_ON_ONCE(folio_test_slab(folio))) >>> return false; >>> @@ -2793,8 +2784,18 @@ static bool gup_fast_folio_allowed(struct folio *folio, unsigned int flags) >>> */ >>> if (secretmem_mapping(mapping)) >>> return false; >>> - /* The only remaining allowed file system is shmem. */ >>> - return !reject_file_backed || shmem_mapping(mapping); >>> + >>> + /* >>> + * If we aren't pinning then no problematic write can occur. A writable >>> + * long term pin is the most egregious case, so this is the one we >>> + * allow only for ... >>> + */ >>> + if ((flags & (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE)) != >>> + (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE)) >>> + return true; >>> + >>> + /* ... hugetlb (which we allowed above already) and shared memory. */ >>> + return shmem_mapping(mapping); >> >> Acked-by: David Hildenbrand (Arm) >> >> I'm wondering if it would be a good idea to check for a hugetlb mapping >> here instead of having the folio_test_hugetlb() check above. >> > > I think it's nice that hugetlb folios are determined immediately to be > eligible for GUP-fast regardless of whether the folio is file-backed or > not. Ok, I'll leave it as is for now. > >> Something to ponder about :) >> >> -- >> Cheers, >> >> David