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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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2db0d124c647e711c0bf95b1c7f1316a0d1408ae.1778616612.git.mst@redhat.com> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 389E710000D X-Stat-Signature: j9t1pym8rxacrtiq4ksnusrowrw9awgn X-Rspam-User: X-HE-Tag: 1778768296-379191 X-HE-Meta: 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 FDAJFByB 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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 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 >