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[80.230.25.21]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488d5cf2e70sm177712665e9.0.2026.04.13.13.32.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 13 Apr 2026 13:32:10 -0700 (PDT) Date: Mon, 13 Apr 2026 16:32:07 -0400 From: "Michael S. Tsirkin" To: "David Hildenbrand (Arm)" Cc: linux-kernel@vger.kernel.org, Andrew Morton , Vlastimil Babka , Brendan Jackman , Michal Hocko , Suren Baghdasaryan , Jason Wang , Andrea Arcangeli , linux-mm@kvack.org, virtualization@lists.linux.dev, Johannes Weiner , Zi Yan Subject: Re: [PATCH RFC 1/9] mm: page_alloc: propagate PageReported flag across buddy splits Message-ID: <20260413163104-mutt-send-email-mst@kernel.org> References: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 1NeB_LCUgIJ1EV0WHD3Whvf-bzj1uCBJDZid3NKRmwA_1776112332 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 3466D100007 X-Stat-Signature: 8i94swcztmarkyob1aa6shcof675rhe9 X-HE-Tag: 1776112336-177836 X-HE-Meta: U2FsdGVkX1/7EHlldqmcIQNg8kUX1sDh9YqJRZDjizLSkRnLghU/WGYpjhAzEwJv3KxhSSpX6pJYKYxwcjkZkgSbzm2jNnkh3G9yi+YS8MTblOvPkWv8Dl9HRkeBa/ChdLK5vrvKkLJ8RXu0bKkcBEgbFMLnBpHO5gaaVkDGgt5/eKHWXBZWhXi1sQ9svgY6uSxrm6w2XPbs7zmCj0ByiIyESMwhRM9VWEEt2YsiBaNA86JE4PG8xsWBjJpmDFEGF5WatMUr7Az6XlC5Wo0DtQI86Nt6KeU7njoIVlCNQcswRcoIvABnRfhP0QXbEzHMXFg6+7bYSaviSA98p/JsEJWEc72rt4GDLB4JVcCYLp/wujNa1IxWXEOQGsdXFEf+6U7bYjP+IwHF30IP8Pd0Oa/BB1DV8UhX5vCMVkZPcGGL3/y1pMSOihzE4pymoW5zqBkSqmADWQIKZ7Ln0WnXgNMzf3Ej6abf/1KOqM7pIASWavDaNI/ZqzI5VUC8MNL4ARngchgZprDBo/9S5Ka0q3e4+c5pg4f8nFod1iVUS3CRYzAUw4Rsm64GU/koB1FQyn5YUyL0OoWB8Tgzzb0bnFWa1UgriQlj6y45IWJQx0RUxkE7f/iXOvydG43FL/uMChwCB2p7GDSrvQi4I8lN576ckC4HPeL8xgbB589hYNzBMSO/nQUN2y8w+sUjzHj+CR9PVXVrbduUca6pPSl4GIcqtnD6wBVpTXpUY9lfq6Lk2neY+upXCYv89/UnJCRl4ANVIVJbPuEd/AbttScov7PXtNsn9SGdlMBIH2SZqob29VhzWiT9pImYuChuzyEHb7O6ajXdw2cOvsNqnjcfaMyyu7V06X+I57AwesyVMgGcEGM/MevZdiHWnKxJEd9D/lyH3SkTiiwZqwRfVIJhn2ksHRnzn+MUC5P1U4PYh0v3uKWfjENn/2CtX1hpxC1kLqdpA/MPIGUP2/b1JDT dru9/AV2 zlkTgR/VASdVCZcbrdOXZXQlH649ssbH/7NzNrGtqFO1YfGf6iDTnxS9h2AwgxCNMHWY3PSPI1dQSn4nwbtnQXW6OxFDUpwya+WxctDwgo5lTZIwTT27Qx8NABM0f5AAgUt75ybcM+Ww+GP7Rbe6S3Tb6tmTWjrYSPgfV/lxHtIHjEpXv+UgWg98HCNzwrmXmPfm2/u7oyDIOGLl98osnNXni3SFHz2Ym6c3/Ll4oUVUEStWtLgkVY1I2uBjYCEvTvKlvwc7m9NiQ/7j+l2P8FWlXt3blj+CMMGwvybfdz+T2lHNyRmLm1ZxTki6IO48TnoEndhX+1lRp5ZbUYqw1610IxnlyOVqd+fDncP+mUQ4DANvr76EkXwRgRAcaqkmeIUjFZQqPxqyaMA5yig4TsMDtKA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Apr 13, 2026 at 09:11:51PM +0200, David Hildenbrand (Arm) wrote: > On 4/13/26 00:50, 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. > > > > Propagate the PageReported flag to sub-pages during expand() so > > that they are recognized as already-reported. > > > > Signed-off-by: Michael S. Tsirkin > > Assisted-by: Claude:claude-opus-4-6 > > --- > > mm/page_alloc.c | 17 ++++++++++++++--- > > 1 file changed, 14 insertions(+), 3 deletions(-) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 2d4b6f1a554e..edbb1edf463d 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -1730,7 +1730,7 @@ struct page *__pageblock_pfn_to_page(unsigned long start_pfn, > > * -- nyc > > */ > > static inline unsigned int expand(struct zone *zone, struct page *page, int low, > > - int high, int migratetype) > > + int high, int migratetype, bool reported) > > { > > unsigned int size = 1 << high; > > unsigned int nr_added = 0; > > @@ -1752,6 +1752,15 @@ static inline unsigned int expand(struct zone *zone, struct page *page, int low, > > __add_to_free_list(&page[size], zone, high, migratetype, false); > > set_buddy_order(&page[size], high); > > nr_added += size; > > + > > + /* > > + * The parent page has been reported to the host. The > > + * sub-pages are part of the same reported block, so mark > > + * them reported too. This avoids re-reporting pages that > > + * the host already knows about. > > + */ > > The comment is a bit excessive. I'd say you can drop it completely. > > > + if (reported) > > + __SetPageReported(&page[size]); > > } > > > > return nr_added; > > @@ -1762,9 +1771,10 @@ 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); > > } > > > > @@ -2322,7 +2332,8 @@ try_to_claim_block(struct zone *zone, struct page *page, > > > > del_page_from_free_list(page, zone, current_order, block_type); > > change_pageblock_range(page, current_order, start_type); > > - nr_added = expand(zone, page, order, current_order, start_type); > > + nr_added = expand(zone, page, order, current_order, start_type, > > + false); > > In MM land we started doing > > /* reported= */false > > > This raises a good question: how does buddy merging handle the reported > flag? > > -- > Cheers, > > David IIUC it doesn't: reported pages are never merged, if a page is merged it has just entered buddy. -- MST