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[71.246.228.50]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8e7d93c2fffsm1070867785a.36.2026.04.21.09.51.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Apr 2026 09:51:02 -0700 (PDT) Date: Tue, 21 Apr 2026 12:51:00 -0400 From: Gregory Price To: "Michael S. Tsirkin" 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: References: <20260420192037-mutt-send-email-mst@kernel.org> <20260421090341-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260421090341-mutt-send-email-mst@kernel.org> X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 105251C000E X-Stat-Signature: 8rsob3uz9psphj9hjrpqe1a9ese5wib6 X-Rspam-User: X-HE-Tag: 1776790263-715520 X-HE-Meta: U2FsdGVkX1/eQpufS4QwM1w5Di1TqvL5rDVtEZ39oqDdhsilKv3ix9LUKmKPEL32omm7lbOlQQbShHlNtJCodp5J8Xw/+Sm8uCyTf82242a+Ygzc+Yfs4zSiDlc9db2aa4bJC/PMCwpVKcSDbVYFOwvhyFLcwMidCLDMK4iRM7+P3bXGiwPS5mFnEAumQXXW5vOnigi0QCkXeaPhTEgRxYZ/YTkpJ0cEUnbDV3dnT93Qyy1qmCVt8KopbHOTpKYGJoLW1fB5xNffB5/At+bgscTRUY6nXyk13EjXuJQP5qiz6VzhPkcJqu0VLlYgLkqptY5sX6tygLC/EQ3P0L3rTauC0WsXeA74fR0vLf2Ub6rxiZd/LXcETR34Yjsqq1GvBneis/FYkUZp7zZEZPaDRgdhO5mHiH3DnHxH3US1Ep2+BEoHHo3xlA3v7ydUMOPGVgcMJ5jtRY2hmTw6j3Ea4JAC5+j6TgLxYupOgyybCrmeycbiifkymGZ38ZgClsC5CBLJ7vcf4oDWdhdsUI8jjc5J1sG89+DmVpQQojcD1tMqzSqgb2RfTG6BfyTpGS8Hll5x3u5IEJaGwDtOb9vTHPxOmYOHy9blUJ3tdoOlvJ22834JPnzAmKc3SME/aqTYSq9ZrV39zDSE0lLHzYKMM1rXL37vpcYReMC7lNG2frea++bUHp6B/7uRqX3zULBAQyaa395Ed0/d9PCMQZyyacnPIB9w5cClIFBoUrgTl0nw0klIsR+Qm62vKdrDourrgtB9D4j4z5KW45s3TU1zT/n3E8KooPGV2JqcnculsTtifcMqxoWM9u9kMDn2g2YEvM95cFiSCUAUMkOBfWT6O0DOHaIoB31WIQkJDo41iO+HRg11Xv1Ma8ujVAXCsWzPTWat3rJCIzv+w8+QAq5HPDoe5Qg1wAIaLbtED+7bXB+KJPwW8OcN6VEqEZgL47gQ0HCB/yck0RskymxT9j2 UQttNfrY uCVccKIa8nRc5aiL72bDT3cSTLs/Ty4kCLANPbz2OZuWYZYQKfO+MdO7vc1l+N4rtUeXYn1Jch9YdGJSyAudr8Hda2jzFRUyUstn45Z/or8KtoVrob9xuvC4bJsd9Ds1zTXJkKMOj8rVx9xA0jNqHCJD0q7kv4E4MOYTxyip+LXrHk2Lvk6VFiInHDSEN/Vt0rnqTzorboP/MUX9Nyu5JeFONrznLZnh/HtRcpD31KOAo52bh0b0OIDUFlbOWlpEH1ft8m0oM4Vweqgp7aYCRMU3Q66e61c6joZIa6ad0dBkMwCLS8ITtNxpHtnFHnmSceU3t97AriTgDtZo= 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 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