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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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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-Queue-Id: 6CF1821109 X-Spam-Score: -3.01 X-Rspamd-Action: no action X-Spamd-Result: default: False [-3.01 / 50.00]; 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MISSING_XM_UA(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.de:dkim,localhost.localdomain:mid] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spam-Flag: NO X-Spam-Level: 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