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Fri, 6 Mar 2026 12:49:17 +0000 (UTC) X-Farcaster-Flow-ID: 3c65634d-d2ee-42b8-a0db-5e2cd1d9a376 Received: from EX19D005EUB003.ant.amazon.com (10.252.51.31) by EX19MTAEUC001.ant.amazon.com (10.252.51.193) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.37; Fri, 6 Mar 2026 12:49:14 +0000 Received: from [192.168.2.180] (10.106.83.26) by EX19D005EUB003.ant.amazon.com (10.252.51.31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.37; Fri, 6 Mar 2026 12:49:09 +0000 Message-ID: Date: Fri, 6 Mar 2026 12:49:08 +0000 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [PATCH v10 04/15] mm/gup: drop local variable in gup_fast_folio_allowed To: "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" 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@suse.cz" , "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" , "shuah@kernel.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" , "ackerleytng@google.com" , "maobibo@loongson.cn" , "prsampat@amd.com" , "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" , "Cali, Marco" References: <20260126164445.11867-1-kalyazin@amazon.com> <20260126164445.11867-5-kalyazin@amazon.com> Content-Language: en-US From: Nikita Kalyazin In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: EX19D015EUB002.ant.amazon.com (10.252.51.123) To EX19D005EUB003.ant.amazon.com (10.252.51.31) On 05/03/2026 19:07, David Hildenbrand (Arm) wrote: > On 1/26/26 17:47, 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 | 19 ++++++++----------- >> 1 file changed, 8 insertions(+), 11 deletions(-) >> >> diff --git a/mm/gup.c b/mm/gup.c >> index 9cad53acbc99..e72dacce3e34 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 +2784,14 @@ 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 long term >> + * pin is the most egregious case so this is the one we disallow. >> + * Also check the only remaining allowed file system - shmem. >> + */ >> + return (flags & (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE)) != >> + (FOLL_PIN | FOLL_LONGTERM | FOLL_WRITE) || shmem_mapping(mapping); > > Best to keep this split and a bit more readable. > > /* > * 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); Makes sense, thank you! > >> } >> >> static void __maybe_unused gup_fast_undo_dev_pagemap(int *nr, int nr_start, > > > -- > Cheers, > > David