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[100.36.248.188]) by smtp.gmail.com with ESMTPSA id af79cd13be357-910ba36e638sm275535485a.9.2026.05.14.08.32.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 14 May 2026 08:32:29 -0700 (PDT) Date: Thu, 14 May 2026 11:32:26 -0400 From: Gregory Price To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, "David Hildenbrand (Arm)" , Jason Wang , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , Muchun Song , Oscar Salvador , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Hugh Dickins , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Ying Huang , Alistair Popple , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Axel Rasmussen , Yuanchu Xie , Wei Xu , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , virtualization@lists.linux.dev, linux-mm@kvack.org, Andrea Arcangeli Subject: Re: [PATCH v7 02/31] mm: page_alloc: propagate PageReported flag across buddy splits Message-ID: References: <20260514104735-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260514104735-mutt-send-email-mst@kernel.org> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: BB01120010 X-Stat-Signature: zer9ese4jxz86prwf7d9yw4wbnhw1qbf X-Rspam-User: X-HE-Tag: 1778772750-303352 X-HE-Meta: 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 L/zh0g6J 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, May 14, 2026 at 10:48:28AM -0400, Michael S. Tsirkin wrote: > On Thu, May 14, 2026 at 07:51:03AM -0400, Gregory Price wrote: > > On Tue, May 12, 2026 at 05:05:16PM -0400, Michael S. Tsirkin wrote: > > > When a reported free page is split via expand() to satisfy a > > > smaller allocation, the sub-pages placed back on the free lists > > > lose the PageReported flag. This means they will be unnecessarily > > > re-reported to the hypervisor in the next reporting cycle, wasting > > > work. > > > > > > While I was unable to quantify the performance difference, it is > > > an obvious waste, even if small. > > > > > > Propagate the PageReported flag to sub-pages during expand(), > > > both in page_del_and_expand() and try_to_claim_block(), so > > > that they are recognized as already-reported. > > > > > > Signed-off-by: Michael S. Tsirkin > > > Assisted-by: Claude:claude-opus-4-6 > > ... snip ... > > > @@ -1731,9 +1740,10 @@ static __always_inline void page_del_and_expand(struct zone *zone, > > > int high, int migratetype) > > > { > > > int nr_pages = 1 << high; > > > + bool was_reported = page_reported(page); > > > > > > __del_page_from_free_list(page, zone, high, migratetype); > > > - nr_pages -= expand(zone, page, low, high, migratetype); > > > + nr_pages -= expand(zone, page, low, high, migratetype, was_reported); > > > account_freepages(zone, -nr_pages, migratetype); > > > } > > > > > > > Maybe mildly out of scope but worth asking: Are there other flags that > > should be retained/propogated on a split? If so, rather than pass > > was_reported, should we just take a temporary copy of the page flags and > > pass them all in? > > > > ~Gregory > > > Not that I can see, no. > You do this exact thing again later :] https://lore.kernel.org/linux-mm/9a22e0f9bbe1278913754db6df76e291a006181a.1778616612.git.mst@redhat.com/ ~Gregory