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Mon, 13 Jan 2025 11:05:21 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id Cr+MLnHzhGf3dQAAD6G6ig (envelope-from ); Mon, 13 Jan 2025 11:05:21 +0000 Date: Mon, 13 Jan 2025 12:05:16 +0100 From: Oscar Salvador To: Peter Xu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Breno Leitao , Rik van Riel , Muchun Song , Naoya Horiguchi , Roman Gushchin , Ackerley Tng , Andrew Morton Subject: Re: [PATCH v2 2/7] mm/hugetlb: Stop using avoid_reserve flag in fork() Message-ID: References: <20250107204002.2683356-1-peterx@redhat.com> <20250107204002.2683356-3-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250107204002.2683356-3-peterx@redhat.com> X-Rspamd-Action: no action X-Stat-Signature: d18iaue7yi7inaaz91jbz3hwghcwz5xe X-Rspam-User: X-Rspamd-Queue-Id: 3A048140010 X-Rspamd-Server: rspam08 X-HE-Tag: 1736766323-495144 X-HE-Meta: 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 YljVfAzT IEVrwIiCszYwt+DfDG5bkRX6kexzOuQqGezz8AVsOL3PMheUJXf7IBG4SMt1inrpeDY7YuoFt7TLZfWKNyQMCv2Fkd+PhwxM6O5EDg0rFbusW4a69jmcLHUUBWhyQn/QSSBq/nh+1aImR4pFQjyFYT/7qiwpKILGGp5OTiMi4X+YoE1WYwhI14F5hyzXXxXrtuJV7HUGfkKg6f1C0BN+uy6sTASNJ2D4dky4TugPY9oJ7Uj8lMeUb34J8yX1KayHghvhd8BHfENbxntd2EYR+rW/J2ug+dQMPPBkICVqDTYhlD9SehZeBePhBp2CGlk3VAJTQFWsNOYWgcdBhvn01OphG1p6JE21eZe34oijMpv+q394hKfrC6YHR550J6zXyw5ZhVSNmdX3/0TEJ0ckHkDyrgw== 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 Tue, Jan 07, 2025 at 03:39:57PM -0500, Peter Xu wrote: > When fork() and stumble on top of a dma-pinned hugetlb private page, CoW > must happen during fork() to guarantee dma coherency. > > In this specific path, hugetlb pages need to be allocated for the child > process. Stop using avoid_reserve=1 flag here: it's not required to be > used here, as dest_vma (which is destined to be a MAP_PRIVATE hugetlb vma) > will have no private vma resv map, and that will make sure it won't be able > to use a vma reservation later. > > No functional change intended with this change. Said that, it's still > wanted to do this, so as to reduce the usage of avoid_reserve to the only > one user, which is also why this flag was introduced initially in commit > 04f2cbe35699 ("hugetlb: guarantee that COW faults for a process that called > mmap(MAP_PRIVATE) on hugetlbfs will succeed"). I don't see whoever else > should set it at all. > > Further patch will clean up resv accounting based on this. > > Signed-off-by: Peter Xu Reviewed-by: Oscar Salvador -- Oscar Salvador SUSE Labs