From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A3440408023 for ; Wed, 10 Jun 2026 13:17:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781097441; cv=none; b=ODEr8JZrYMamT0xH3uEr2YzfazE5JANV7X8cXDJI0u8LBuKlRdx0/OkKcGhG024QM8dm0ZfY1DCS78hxEUBNjJyfjNAmdFB4UGBlcH1TDSWUAWHWRbkeX0TnzfOiq86yZpXdVZ3BxXKp/Vg549WNAVxYiHIME4LKe9wvUfTcymg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781097441; c=relaxed/simple; bh=1D9+hklB7r3x0u0ch2J4IhAFeDFpVae4jEVnWDHzGsA=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition; b=VHARwL3cshcDClKXqSG6W/tJAsHLbWoZvHzWN0LVO1lupGEhyiuK0oTzbm/0G1//CwwC53XOO6amZQh9kaCJ3vwHJioSdl4jYqca04o0aliU6MPcZe35bCgIkn3rR9pYC/mo8pYkl6Taw54XmCFndTsEj7Ca0Hj0jUOFI8ezWro= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=ipUOx04h; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=TQG6XCD3; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ipUOx04h"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="TQG6XCD3" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1781097437; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type; bh=JIynXs9jKTkZFqI4maeQsdqviVHDwx4+PYnRpWMJtSw=; b=ipUOx04hIZPPGb7N6wPk8WJ17+noyrP69fyPWOcbt/2eiYod6b88tLSHgIYisYL4e4Vxlo /1HsAmKiKbhAaJPELNOnTSg3ksD0BTBf5eA8c47jbvqCUt7OzjyFq6ZVX7GHbal4hguRzW 09psHfoo+R+YYTwhvgm3l6cAGPqG/BU= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-347-sxpuWED9Otmy5cN4eBxwBg-1; Wed, 10 Jun 2026 09:17:16 -0400 X-MC-Unique: sxpuWED9Otmy5cN4eBxwBg-1 X-Mimecast-MFC-AGG-ID: sxpuWED9Otmy5cN4eBxwBg_1781097435 Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-490ae0167ceso31880315e9.1 for ; Wed, 10 Jun 2026 06:17:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1781097435; x=1781702235; darn=vger.kernel.org; h=content-disposition:mime-version:message-id:subject:cc:to:from:date :from:to:cc:subject:date:message-id:reply-to; bh=JIynXs9jKTkZFqI4maeQsdqviVHDwx4+PYnRpWMJtSw=; b=TQG6XCD3ix4jVKKfH0qtbxdL12tuM6ZPkVcqyMBwJxLKY4Zdai5dVlNkfiytSm/N6W OE+KVD0qMLcrO/kKAfzyvnA920EgzK71I6utWlUOEblIsBu1u2BvJNfCYygmERLX6qN4 Q7NtTvx35p97MA64spEHIZniXwb0WXodfva70N3/5yfNUs2elWVzOMATz3DtgZNniPRW xCm4UhV5SR7HTOcagtWTmNGYaWUUxsKuAPKvOnSMGLq/yoaRNtDo2d1mX+8QAojcXjmX Qi8FlZR6D7isUn0VdZ5BT0pSm2NRYTjbT1NBUinNRAmAiVBHOFKnQBU2UFWTuAV1B6+4 cwpg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1781097435; x=1781702235; h=content-disposition:mime-version:message-id:subject:cc:to:from:date :x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=JIynXs9jKTkZFqI4maeQsdqviVHDwx4+PYnRpWMJtSw=; b=o0F9+4dsJUrmRztQ3YDb51IDI5cgTh3l1Fxyl1IiuE5dNua733gDsAAbR25aTLP9XY NP15u3PIxY6FzsXQistnnVekRsq3PSlWHQUjY63LvcV8esFC7QzigJH7UxPRD3cNc14t /d5P8xe9OMQS2JWRL8vpw9qExi8ONRq7Vc9I2ZBBmASX22AVVxuW77YqkaqCiuexZoTC 3EupTO9ZjjrqPI4JnCYKoXNlPSFyAkFMV0tU6DuYSWtDWjsgTcGMtS2j3+JOUAu1fT1Y crXbZmLjK1Ne4xvQnlVIpdzzGn74cHfUOMPOuoY7eozTwVlAUsf8S0yyFGRafxcxRQc2 94dw== X-Gm-Message-State: AOJu0YzLIeM7sbSQXB5d7aznUtfEI9vbpVT9vGDApdYLvm1xSUEq9L7c IproK50lKJ7Padc4kiAzrO+ScvXdrEam/6lDsab6YSTptMwPkicACbypDaB8GTMufcqBwjohiYh /ZoR86GWT9wimyXHpQj9G92Imqv6olAx776TkVtZUDknuD3smGTD4BwSdVbtPps5kZhb+UCeeeS MrDzE41++04TKJR2Vg/pDKQh2p1L0DShHIaC0Su5AEvn4= X-Gm-Gg: Acq92OFbG/s9hmU5GdkAeE/SbcKPwZHjV3WpKE8x2YUVlrYxzYRwCdAp9Hxj5LqfLXr jU9o8w9FMIKmaM8ZasvBOTiM+JT9dYabAsQh88zECW11n0mCMNAd8z9BZqm8P5sN46On7q+PP9l n36nUI6NjErOoW8lThZrebzJs8UZ/gXuHHhgCYYePiwCdt3t3IENojy7b2FTKtBn9ypqlCmKRlL vtz7nZKxZLI9UOIARakdrqkYUVNey9U99SSCTqkQg2ZQhQsZx8JMmqL5++mo0rNH/qC1Jrpp+rV CNVNNUjSLzuSuiz0F4R7L4YIM7ARfE+SHPIQteeylQJWLkEdNkTsQtWlZgS+Yiku+ohuc44YMIN VLaPIGm1GXV26AsllHFQHiwjSohpdwkW3Py8gXvOKjgR3d82CZctE4Q== X-Received: by 2002:a05:600c:c491:b0:490:bb44:3f8b with SMTP id 5b1f17b1804b1-490c2605385mr407783565e9.17.1781097434866; Wed, 10 Jun 2026 06:17:14 -0700 (PDT) X-Received: by 2002:a05:600c:c491:b0:490:bb44:3f8b with SMTP id 5b1f17b1804b1-490c2605385mr407782215e9.17.1781097434064; Wed, 10 Jun 2026 06:17:14 -0700 (PDT) Received: from redhat.com (IGLD-80-230-85-71.inter.net.il. [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: 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 X-Mailer: git-send-email 2.51.2.2891.g4157995a80.dirty X-Mutt-Fcc: =sent 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