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[100.36.248.188]) by smtp.gmail.com with ESMTPSA id af79cd13be357-910bd620fbcsm229997985a.42.2026.05.14.04.51.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 14 May 2026 04:51:06 -0700 (PDT) Date: Thu, 14 May 2026 07:51:03 -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: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: s5tz84q6m5y1wb9ui4mrguaxoba118i1 X-Rspamd-Queue-Id: F22414000E X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1778759467-458073 X-HE-Meta: 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 bCwwZxf3 +MRObjONXq9zU4VWZErKii10CF/fslMXyiOUxiV6uGvFefDMhmSPmI2zbg70C0JMYKz60PPBrajCdfsu//10KJHJlB0o1lyzpg1CATRrsGD2unk9V+bPszzZEFP3g5/691/kt8OL0RZHxBEXbQ3e7vITfaX4yYhvnm0rfhkKOXosII6zkw7pbNxbuVTwAxlPrJ+mjv3HK/KFdHagUJT8L6GK4UJTfXW+c5SgBARCfGWy6dzfBev45CnlK1+rXuowl/ZRlgtNGc5USAiV/viEmTTY4TGGvrZTEz00EwY6GofDJBddCxPTqTL5gkQS6vi5fsqqmgt3b91m278b4QZRZxh8idZ0Hz5tDRcexstd5x98m4fwnijM74wj3w64/PCmREi2ENymrJ1vDrZqNvAHvqrtec5xKvbUCPPKIt5desd/9WdB8WubR1KvYQ9sYmWBdy3yfRn2ynjs3dVnZuBcksDwPdA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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