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[80.230.25.21]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488fb7c0eacsm116411425e9.35.2026.04.21.06.03.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Apr 2026 06:03:16 -0700 (PDT) Date: Tue, 21 Apr 2026 09:03:12 -0400 From: "Michael S. Tsirkin" To: "Huang, Ying" Cc: linux-kernel@vger.kernel.org, Andrew Morton , David Hildenbrand , Vlastimil Babka , Brendan Jackman , Michal Hocko , Suren Baghdasaryan , Jason Wang , Andrea Arcangeli , linux-mm@kvack.org, virtualization@lists.linux.dev, Johannes Weiner , Zi Yan , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Alistair Popple Subject: Re: [PATCH RFC v2 02/18] mm: add pghint_t type and vma_alloc_folio_hints API Message-ID: <20260421090238-mutt-send-email-mst@kernel.org> References: <290d615a001cf121dc0c604eb79451bcc7917baa.1776689093.git.mst@redhat.com> <87pl3ti0x8.fsf@DESKTOP-5N7EMDA> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <87pl3ti0x8.fsf@DESKTOP-5N7EMDA> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: PmxyI4aMzY6XpnkiM-VJu19m7wrkPXLbNfk-4o8FxMY_1776776599 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Apr 21, 2026 at 08:58:59AM +0800, Huang, Ying wrote: > "Michael S. Tsirkin" writes: > > > Add pghint_t, a bitwise type for communicating page allocation hints > > between the allocator and callers. Define PGHINT_ZEROED to indicate > > that the allocated page contents are known to be zero. > > > > Add _hints variants of the allocation functions that accept a > > pghint_t *hints output parameter: > > > > vma_alloc_folio_hints() -> folio_alloc_mpol_hints (internal) > > -> __alloc_frozen_pages_hints() > > > > The existing APIs are unchanged and continue to work without hints. > > For now, hints is always initialized to 0. A subsequent patch will > > set PGHINT_ZEROED when the page was pre-zeroed by the host. > > Why do we need this feature? Is there any performance impact? If so, > please provide some performance data. It's in the cover letter: Performance with THP enabled on a 2GB VM, 1 vCPU, allocating 256MB of anonymous pages: metric baseline optimized delta task-clock 191 +- 31 ms 60 +- 35 ms -68% cache-misses 1.10M +- 460K 269K +- 31K -76% instructions 4.54M +- 275K 4.10M +- 130K -10% With hugetlb surplus pages: metric baseline optimized delta task-clock 183 +- 24 ms 45 +- 23 ms -76% cache-misses 1.27M +- 544K 270K +- 16K -79% instructions 5.37M +- 254K 4.94M +- 155K -8% > [snip] > > --- > Best Regards, > Huang, Ying