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Tue, 3 Jun 2025 05:43:22 +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 taubCXqLPmi5bQAAD6G6ig (envelope-from ); Tue, 03 Jun 2025 05:43:22 +0000 Date: Tue, 3 Jun 2025 07:43:16 +0200 From: Oscar Salvador To: Jann Horn Cc: Andrew Morton , Muchun Song , linux-mm@kvack.org, Lorenzo Stoakes Subject: Re: [PATCH] hugetlb: block hugetlb file creation if hugetlb is not set up Message-ID: References: <20250528-hugetlb-nerf-v1-1-a404ca33e819@google.com> <20250602204107.177e2fdf2209b0926b5ce28e@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Action: no action X-Stat-Signature: u7y37mgs3wwas7do848gn4cgchjni9uq X-Rspamd-Queue-Id: 580C04000A X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1748929404-874926 X-HE-Meta: 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 mx3NO0uE mu5ea4el6KrmTwVxWG7II2s/rj5oO0D+LOYJdLOFdpgJeKVPsTqe3mA88K93RhUgOUQ3+Oe4eWb4iha0wMos1ERowhn7t2W/wU32EalfuV2zXbbufRbqPbTnAQmf16aPCsHPvJsB0Ur5lluOvcTt/VOcUupab+fulYmEACq7egN2kh64AJ4WiHsDXrvrPrz9EgtLazwokLA8mKY/5jbzI/B5QrXDIeS5fautXyE8YEHBLUgRUclQ2QkVnl6UATq/rANu4 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, Jun 03, 2025 at 06:29:24AM +0200, Jann Horn wrote: > Yes, this change changes kernel behavior that is userspace-visible, > and causes syscalls to return errors where they worked before. Yes, that is what make me unease about this. It is true that most of the hugetlb cases out there work on pre-allocated pages, because the later it gets the harder to get large pages from the system. But as you say below, there might be applications out there that tweak the sys knobs themselves, and with this change those might break. Now, how valid are those? Heh, hard to anwser. So I guess it boils down to how hard and effective is to actually exploit whatever we manage to create by allowing this. But if we take that route, I think that hinting the user about this behaviour change is the right thing to do. -- Oscar Salvador SUSE Labs