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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42f7cc090bdsm11152502f8f.19.2025.12.05.13.49.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Dec 2025 13:49:41 -0800 (PST) Date: Fri, 5 Dec 2025 21:49:40 +0000 From: David Laight To: Lorenzo Stoakes Cc: Andrew Morton , David Hildenbrand , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , oliver.sang@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: avoid use of BIT() macro for initialising VMA flags Message-ID: <20251205214940.211a2de2@pumpkin> In-Reply-To: <4eea9138-3853-457d-9113-e3caa7f00437@lucifer.local> References: <20251205175037.1287366-1-lorenzo.stoakes@oracle.com> <20251205184342.2cfcc73e@pumpkin> <4eea9138-3853-457d-9113-e3caa7f00437@lucifer.local> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: A0F9D20006 X-Rspamd-Server: rspam10 X-Stat-Signature: erw76qgowokegufgqf4y759ucszwkgja X-HE-Tag: 1764971383-704673 X-HE-Meta: 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 EJ9ytGCp Sb5i9xJFtVGB5HKCk83jPBY7+I2eLQPN5qxEU0Ufun/cGGVOPa03qDyx2RndCh9jo7ucf/QpG/VjKCqUvJk6GJF05vpvmYw1ZnWfBLr3Izwwzux8Q2i6J4slnC8e6JeORX8gEal5vetbM3twQOuuMG0KVd4uVCXAYdbSdNEGJuFu95cjMPwcHjHsfmTliYHyojTOl42vvEdd01bjEfq1wh7R06QL3U6p1MRwD2uoYWR5Xay9NNjVoPiaoL5M76MVEHYrdqX80Y/nKslNwqsq2rEAE9d5AcwYyxsnPjpgPBYImlkT2OMqS+7lRqpVKkvOpMw+8vr3Ke0i5P1JYISNG2jULUL+t9RRe8mohFsrFN55jQS9Bhq2S10S8ZHxuE9nXDNuOCOQJhjzfVPD26XXvTd08bJZR2Js3fBXdoP5Jiz2LE+dQiAG86Mlz2Po+lkIsTLs0pXqSLF8gqtU= 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: List-Subscribe: List-Unsubscribe: On Fri, 5 Dec 2025 19:18:56 +0000 Lorenzo Stoakes wrote: > On Fri, Dec 05, 2025 at 06:43:42PM +0000, David Laight wrote: > > On Fri, 5 Dec 2025 17:50:37 +0000 > > Lorenzo Stoakes wrote: > > > > > Commit 2b6a3f061f11 ("mm: declare VMA flags by bit") significantly changed > > > how VMA flags are declared, utilising an enum of VMA bit values and > > > ifdef-fery VM_xxx flag declarations via macro. > > > > > > As part of this change, it uses INIT_VM_FLAG() to define VM_xxx flags from > > > the newly introduced VMA bit numbers. > > > > > > However, use of this macro results in apparently unfortunate macro > > > expansion and resulted in a performance degradation.This appears to be due > > > to the (__force int), which is required for the sparse typechecking to > > > work. > > > > Does sparse complain if you just add 0? As in: > > #define INIT_VM_FLAG(name) BIT(VMA_ ## name ## _BIT + 0u) > > > > That should change the type without affecting what BIT() expands to. > > Thanks, checked that and unfortunately that doesn't satisfy sparse :) Oh - it is that __bitwise that causes grief. > I don't think it's too crazy to use 1UL << here, just very frustrating (TM) > that this is an issue. Did you try getting DECLARE_VMA_BIT to define both the bit number and the bit flag and put them both into the anonymous enum? Or are there other reasons for not doing that? > > Add rant about the compiler thinking anon enums are doing anything other than defining constants. David > > Cheers, Lorenzo