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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uArC8-00000002UIK-3S4j; Fri, 02 May 2025 14:16:52 +0000 Date: Fri, 2 May 2025 15:16:52 +0100 From: Matthew Wilcox To: Lorenzo Stoakes Cc: Ignacio.MorenoGonzalez@kuka.com, Liam.Howlett@oracle.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: mmap: map MAP_STACK to VM_NOHUGEPAGE only if THP is enabled Message-ID: References: <20250502-map-map_stack-to-vm_nohugepage-only-if-thp-is-enabled-v1-1-113cc634cd51@kuka.com> <3de8814b-9964-489c-8d13-feb319623b82@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3de8814b-9964-489c-8d13-feb319623b82@lucifer.local> X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 4FC9F100002 X-Stat-Signature: m94inx3dzchdkd8mqesdhodibjrgdi6n X-Rspam-User: X-HE-Tag: 1746195432-716926 X-HE-Meta: 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 PXfXJiD8 0IpeJ7Y1FEW9aidkyCbOgftAFjg4OaOrppg9HjlR2LmVra/Ldk2tHFnIQgh94gOghpXBrMsh/y4nXlnVD5wawOyyow7VlfzxMgjkBOmMl9vKWOAimUKUQM251fFdqK4XC7ThprfKHtUL8Y0Omjy3KGrBK75EeJAcDeAJcI1d8tjqT7mpBlly0Ff/uU6Q7KBAKW6rCy4U2axAGrZxLkaPbfurx0gJxDXid2LpC4IGVK1xviFqU3+h8TbNS/P8Y8VNz5UHkJNbc5JF5qTRJy32oxfLo2PkaLjC5QmUfUJbTqiTeyZBANhcIHIwzVFi9QU9yDMC+I1q0+3hz4LI= 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, May 02, 2025 at 02:12:16PM +0100, Lorenzo Stoakes wrote: > On Fri, May 02, 2025 at 02:03:48PM +0100, Matthew Wilcox wrote: > > On Fri, May 02, 2025 at 11:31:41AM +0200, Ignacio Moreno Gonzalez via B4 Relay wrote: > > > From: Ignacio Moreno Gonzalez > > > > > > commit c4608d1bf7c6 ("mm: mmap: map MAP_STACK to VM_NOHUGEPAGE") maps > > > the mmap option MAP_STACK to VM_NOHUGEPAGE. This is also done if > > > CONFIG_TRANSPARENT_HUGETABLES is not defined. But in that case, the > > > VM_NOHUGEPAGE does not make sense. For instance, when calling madvise() > > > with MADV_NOHUGEPAGE, an error is always returned. > > > > Isn't that the real problem though? > > Hmm, but wouldn't we want users who are trying to set MADV_[NO]HUGEPAGE to > be made aware that it isn't going to do anything? ... I thought the patch was clear. Only setting NOHUGEPAGE becomes a no-op. Setting HUGEPAGE remains EINVAL. > And wouldn't changing this be a possibly 'breaking userspace' thing if > somebody somewhere relies on this? I don't see what userspace could rely on it returning EINVAL, since it won't on a kernel which has THP enabled. > Also this will make this inconsistent with e.g. MADV_COLLAPSE also? Not sure how ...