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[100.36.248.188]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-516460cda02sm17671591cf.18.2026.05.14.07.18.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 14 May 2026 07:18:14 -0700 (PDT) Date: Thu, 14 May 2026 10:18:12 -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 25/31] mm: page_alloc: propagate PG_zeroed in split_large_buddy Message-ID: References: <2db0d124c647e711c0bf95b1c7f1316a0d1408ae.1778616612.git.mst@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2db0d124c647e711c0bf95b1c7f1316a0d1408ae.1778616612.git.mst@redhat.com> On Tue, May 12, 2026 at 05:07:20PM -0400, Michael S. Tsirkin wrote: > When splitting a large buddy page, propagate the PG_zeroed flag > to each sub-page before freeing it. __free_pages_prepare clears > all flags (including PG_zeroed), so the flag must be re-set on > each fragment after the split. This ensures that the buddy merge > logic can see PG_zeroed on pages that were part of a larger > zeroed block. > > Signed-off-by: Michael S. Tsirkin > Assisted-by: Claude:claude-opus-4-6 > Assisted-by: cursor-agent:GPT-5.4-xhigh Reviewed-by: Gregory Price > --- > mm/page_alloc.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 468e8bde7d34..ce43f5a3dbaa 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1523,6 +1523,7 @@ static void split_large_buddy(struct zone *zone, struct page *page, > unsigned long pfn, int order, fpi_t fpi) > { > unsigned long end = pfn + (1 << order); > + bool zeroed = PageZeroed(page); > > VM_WARN_ON_ONCE(!IS_ALIGNED(pfn, 1 << order)); > /* Caller removed page from freelist, buddy info cleared! */ > @@ -1534,6 +1535,8 @@ static void split_large_buddy(struct zone *zone, struct page *page, > do { > int mt = get_pfnblock_migratetype(page, pfn); > > + if (zeroed) > + __SetPageZeroed(page); > __free_one_page(page, pfn, zone, order, mt, fpi); > pfn += 1 << order; > if (pfn == end) > -- > MST >