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Wed, 12 Nov 2025 11:56:55 +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 6YJwLwd2FGmJFQAAD6G6ig (envelope-from ); Wed, 12 Nov 2025 11:56:55 +0000 Date: Wed, 12 Nov 2025 12:56:49 +0100 From: Oscar Salvador To: "David Hildenbrand (Red Hat)" Cc: Hugh Dickins , Muchun Song , Deepanshu Kartikey , Vivek Kasireddy , baolin.wang@linux.alibaba.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+f64019ba229e3a5c411b@syzkaller.appspotmail.com Subject: Re: [PATCH] mm/memfd: clear hugetlb pages on allocation Message-ID: References: <20251112031631.2315651-1-kartikey406@gmail.com> <2a10f8c9-dbdf-7bac-b387-e134890983df@google.com> <6a63dbb8-58f7-4511-8090-18a58c3206d8@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6a63dbb8-58f7-4511-8090-18a58c3206d8@kernel.org> X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 315E01C0003 X-Stat-Signature: z4jni4ijcdsrsxseihibmnnm3anetkut X-Rspam-User: X-HE-Tag: 1762948617-171062 X-HE-Meta: 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 1gfCHX+k CM96uVNY3tJULNBVN7TCC7e/xLMWiWaBBBFROAYM8ufoDQc9tvvjgZGlPABxlFpDKPjP5jtxASNPVQhA0M1HlCW9UHueeI23IenBi4ZmEo+jr7JzFNbVE5QlTpq+oTG/cH6L9/D0DOsXmFpZqtQIkLLRroidkncbP5eLzfER7rk1ARM+x7sbrclE0flqrJNgwgTjVDyp1mcrsymzKVhazXHtfi7wtUaLF7OIxzdDp3AQOyOPNIL+XJIQAds9OSfKmuAJTsQs+O0iixkQjJABxzfJYkaD9yT/S639JZ3gkwqwLzig6Bs+zCmm520IEvh5T0h1jzVq1Npz41mKlzEFc7fWr0IjcWF3hQWfQ 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 Wed, Nov 12, 2025 at 11:09:51AM +0100, David Hildenbrand (Red Hat) wrote: > On 12.11.25 10:13, Oscar Salvador wrote: > > memfd_alloc_folio() seems to try to recreate what hugetlb_no_page() > > would do (slightly different though). > > Can we factor that out to merge both paths? I guess it is worth looking into it, I shall fiddle with it. > > Regarding the uptodate question, I do not see what is special about this situation > > that we would not need it. > > We seem to be marking the folio uptodate every time we do allocate a folio __and__ > > before adding it into the pagecache (which is expected, right?). > > Right, at least filemap.c heavily depends on it being set (I don't think > hugetlb itself needs it). Yes, you are probably right. > > Now, for the GFP_ZERO question. > > This one is nasty. > > hugetlb_reserve_pages() will allocate surplus folios without zeroing, but those > > will be zeroed in the faulting path before mapping them into userspace pagetables > > (see folio_zero_user() in hugetlb_no_page()). > > So unless I am missing something we need to zero them in this case as well. > > I assume we want to avoid GFP_ZERO and use folio_zero_user(), which is > optimized for zeroing huge/gigantic pages. Yes, I would go with folio_zero_user() as well, to match what we do in all paths. Maybe if we can factor it out, we can simplifiy it as right now seems a small-duplication of hugetlb_no_page (and more so once we add what is missing: mutex, uptodate and folio_zero_user). -- Oscar Salvador SUSE Labs