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[80.230.85.71]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-490bc3b5b82sm595285305e9.1.2026.06.10.06.17.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Jun 2026 06:17:13 -0700 (PDT) Date: Wed, 10 Jun 2026 09:17:08 -0400 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Miaohe Lin , "David Hildenbrand (Arm)" , Jason Wang , Xuan Zhuo , Eugenio Perez , 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 , Gregory Price , 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 , Naoya Horiguchi , Alexander Duyck Subject: [PATCH v2] mm: page_reporting: allow driver to set batch capacity Message-ID: MIME-Version: 1.0 X-Mailer: git-send-email 2.51.2.2891.g4157995a80.dirty X-Mutt-Fcc: =sent X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: aFLQhAEG4IIt-ooO3eUob1C_aEG-DgqvmlZBgwB8liQ_1781097435 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 2B1DCC0008 X-Stat-Signature: 7a3zq3pm7e3kxdndos7xhjt99zdqqw3t X-HE-Tag: 1781097437-412895 X-HE-Meta: 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 GmgFUqGV Z3otON+i+I5LvnMHkp7uOYK/BiQ/BBHD1WUCyVyvccLAvqm7nqg4O8+aKQ5cV73cB64u3YSHLnGfZmVYYjr/PSbmPhyqAaQ4ZQLX/qsTsL+1PbX/3FTNMn1JbHxvYresV1QZndBFRv+zzH4xBRz2BI5zPBL7cmVRFctpFyyPTeyOZuE2B11sPJMMJJ8GPxas0+k1e+Svuk8q1VZmgpDOirlZ+Gcm+TYzJjrfaklQBn4dCFrWH9dS8PD+ya1S88oqv5fzwo/4q1v9ub+56pFATxLT2NZbwziUBFhsoPzghaEzbXFmzesJBrpCTb/PoNTOr6DbIJxWWp2iBJBAcgQffNrnWZAJFnUtsm3cv7eyeWDwy2KqpcofjEYeLItoGf74gmHb+WgrbCTxeMpg600Xh6vinAfIU05H3skh7q8VFxmv3F63xgDJwpZnj3rxUe0KGzj+m Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: At the moment, if a virtio balloon device has a page reporting vq but its size is < PAGE_REPORTING_CAPACITY (32), the balloon driver fails probe. But, there's no way for host to know this value, so it can easily create a smaller vq and suddenly adding the reporting capability to the device makes all of the driver fail. Not pretty. Add a capacity field to page_reporting_dev_info so drivers can control the maximum number of pages per report batch. In virtio-balloon, set the capacity to the reporting virtqueue size, letting page_reporting adapt to whatever the device provides. Capacity need not be a power of two. Code previously called out division by PAGE_REPORTING_CAPACITY as cheap since it was a power of 2, but no performance difference was observed with non-power-of-2 values. If capacity is 0 or exceeds PAGE_REPORTING_CAPACITY, it defaults to PAGE_REPORTING_CAPACITY. The 0 check and the clamping is done in page_reporting_register(), before the reporting work is scheduled, so we never get division by 0. Fixes: b0c504f15471 ("virtio-balloon: add support for providing free page reports to host") Signed-off-by: Michael S. Tsirkin Assisted-by: Claude:claude-opus-4-6 --- Changes v1->v2: - Document capacity=0 as default in commit log - Document that capacity need not be a power of two - Drop unnecessary comment about integer division cost - Update comment on capacity field: "0 (default) means PAGE_REPORTING_CAPACITY" drivers/virtio/virtio_balloon.c | 5 +---- include/linux/page_reporting.h | 3 +++ mm/page_reporting.c | 24 ++++++++++++------------ 3 files changed, 16 insertions(+), 16 deletions(-) diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index f6c2dff33f8a..6a1a610c2cb1 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -1017,10 +1017,6 @@ static int virtballoon_probe(struct virtio_device *vdev) unsigned int capacity; capacity = virtqueue_get_vring_size(vb->reporting_vq); - if (capacity < PAGE_REPORTING_CAPACITY) { - err = -ENOSPC; - goto out_unregister_oom; - } vb->pr_dev_info.order = PAGE_REPORTING_ORDER_UNSPECIFIED; @@ -1041,6 +1037,7 @@ static int virtballoon_probe(struct virtio_device *vdev) vb->pr_dev_info.order = 5; #endif + vb->pr_dev_info.capacity = capacity; err = page_reporting_register(&vb->pr_dev_info); if (err) goto out_unregister_oom; diff --git a/include/linux/page_reporting.h b/include/linux/page_reporting.h index 9d4ca5c218a0..048578118a4b 100644 --- a/include/linux/page_reporting.h +++ b/include/linux/page_reporting.h @@ -22,6 +22,9 @@ struct page_reporting_dev_info { /* Minimal order of page reporting */ unsigned int order; + + /* Max pages per report batch; 0 (default) means PAGE_REPORTING_CAPACITY */ + unsigned int capacity; }; /* Tear-down and bring-up for page reporting devices */ diff --git a/mm/page_reporting.c b/mm/page_reporting.c index 7418f2e500bb..942e84b6908a 100644 --- a/mm/page_reporting.c +++ b/mm/page_reporting.c @@ -173,11 +173,8 @@ page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone, * any pages that may have already been present from the previous * list processed. This should result in us reporting all pages on * an idle system in about 30 seconds. - * - * The division here should be cheap since PAGE_REPORTING_CAPACITY - * should always be a power of 2. */ - budget = DIV_ROUND_UP(area->nr_free, PAGE_REPORTING_CAPACITY * 16); + budget = DIV_ROUND_UP(area->nr_free, prdev->capacity * 16); /* loop through free list adding unreported pages to sg list */ list_for_each_entry_safe(page, next, list, lru) { @@ -222,10 +219,10 @@ page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone, spin_unlock_irq(&zone->lock); /* begin processing pages in local list */ - err = prdev->report(prdev, sgl, PAGE_REPORTING_CAPACITY); + err = prdev->report(prdev, sgl, prdev->capacity); /* reset offset since the full list was reported */ - *offset = PAGE_REPORTING_CAPACITY; + *offset = prdev->capacity; /* update budget to reflect call to report function */ budget--; @@ -234,7 +231,7 @@ page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone, spin_lock_irq(&zone->lock); /* flush reported pages from the sg list */ - page_reporting_drain(prdev, sgl, PAGE_REPORTING_CAPACITY, !err); + page_reporting_drain(prdev, sgl, prdev->capacity, !err); /* * Reset next to first entry, the old next isn't valid @@ -260,13 +257,13 @@ static int page_reporting_process_zone(struct page_reporting_dev_info *prdev, struct scatterlist *sgl, struct zone *zone) { - unsigned int order, mt, leftover, offset = PAGE_REPORTING_CAPACITY; + unsigned int order, mt, leftover, offset = prdev->capacity; unsigned long watermark; int err = 0; /* Generate minimum watermark to be able to guarantee progress */ watermark = low_wmark_pages(zone) + - (PAGE_REPORTING_CAPACITY << page_reporting_order); + (prdev->capacity << page_reporting_order); /* * Cancel request if insufficient free memory or if we failed @@ -290,7 +287,7 @@ page_reporting_process_zone(struct page_reporting_dev_info *prdev, } /* report the leftover pages before going idle */ - leftover = PAGE_REPORTING_CAPACITY - offset; + leftover = prdev->capacity - offset; if (leftover) { sgl = &sgl[offset]; err = prdev->report(prdev, sgl, leftover); @@ -322,11 +319,11 @@ static void page_reporting_process(struct work_struct *work) atomic_set(&prdev->state, state); /* allocate scatterlist to store pages being reported on */ - sgl = kmalloc_objs(*sgl, PAGE_REPORTING_CAPACITY); + sgl = kmalloc_objs(*sgl, prdev->capacity); if (!sgl) goto err_out; - sg_init_table(sgl, PAGE_REPORTING_CAPACITY); + sg_init_table(sgl, prdev->capacity); for_each_zone(zone) { err = page_reporting_process_zone(prdev, sgl, zone); @@ -377,6 +374,9 @@ int page_reporting_register(struct page_reporting_dev_info *prdev) page_reporting_order = pageblock_order; } + if (!prdev->capacity || prdev->capacity > PAGE_REPORTING_CAPACITY) + prdev->capacity = PAGE_REPORTING_CAPACITY; + /* initialize state and work structures */ atomic_set(&prdev->state, PAGE_REPORTING_IDLE); INIT_DELAYED_WORK(&prdev->work, &page_reporting_process); -- MST