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[80.230.25.21]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488fc140c82sm350387875e9.12.2026.04.21.09.59.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Apr 2026 09:59:35 -0700 (PDT) Date: Tue, 21 Apr 2026 12:59:32 -0400 From: "Michael S. Tsirkin" To: Gregory Price Cc: "David Hildenbrand (Arm)" , linux-kernel@vger.kernel.org, Andrew Morton , Vlastimil Babka , Brendan Jackman , Michal Hocko , Suren Baghdasaryan , Jason Wang , Andrea Arcangeli , linux-mm@kvack.org, virtualization@lists.linux.dev Subject: Re: [PATCH RFC v2 00/18] mm/virtio: skip redundant zeroing of host-zeroed reported pages Message-ID: <20260421125842-mutt-send-email-mst@kernel.org> References: <20260420192037-mutt-send-email-mst@kernel.org> <20260421090341-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 4cUl11W_MGySLug9-DFcQq-7PjeP87zJhmQiqjbCsKY_1776790777 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Queue-Id: E0D3440012 X-Rspamd-Server: rspam12 X-Stat-Signature: 4eedkgqtssjfd96q9zyzgg7buxnirp4q X-Rspam-User: X-HE-Tag: 1776790781-92764 X-HE-Meta: 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 fesY3L0r mzsoqKr7ddfQ0apRee6Jt8JnuPfNeUq+F9QrCWwC0UVgefVzTakRkBcIc3pUdbrJNNivfzEg3/l/qzYlExr48rEWeOkjxtBzoXvGn4MBjUBXtQ/wryaz/Dj9LaM8ho7nYMBBp1kx8V7Sw8CBhb5uDS7zGRhKd5CCNJGyvtU3dBuE49Q95ExUFesGktkQW7YaAtDtBhGzr02h21EvMeREFfsePtokV4ztE5sgwnFk2odXx5TZIq8XBsvLM0UUE8r3nC0Qv2Y0r/bAqTOZlGId0d4c9nqGTnJy0W34h6U/mltl7FAY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Apr 21, 2026 at 12:51:00PM -0400, Gregory Price wrote: > On Tue, Apr 21, 2026 at 09:06:00AM -0400, Michael S. Tsirkin wrote: > > On Mon, Apr 20, 2026 at 10:38:19PM -0400, Gregory Price wrote: > > > > > > Can we leave folio_zero_user() callers the same, but add a PG_zeroed > > > check in folio_zero_user() that skips the zeroing (but not the cache > > > flush) and clear the PG_zeroed bit? > > > > > > Is this feasible? > > > > I do not see how - this would require leaking the page flag out of the > > buddy allocator. > > > > Right, but you're leaking that bit of information out one way or another > - whether it's a page-flag or something else (pghint_t) you have the > same lifecycle problems (when does it become invalidated? how long can > it be trusted for?). > > I suppose at least with (pghint_t) the data (in theory) falls out of > scope and doesn't live with the page - but guaranteed it just ends up > polluting more and more interfaces. > > I'm seeing why David's suggest to plumb __GFP_ZERO correctly makes > sense, it's really the only feasible approach here that doesn't generate > a staleness problem with whatever information you try to leak out. > > ~Gregory OK, v3 with that incoming.