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 03A911A6815 for ; Thu, 21 May 2026 14:09:26 +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=1779372568; cv=none; b=CNieLSiWf/5v7PHvN/jFoKa2o8TxbIeMx4BDYHE3pmIDr5J7KUMsBPQfCcsHvtk3Hfxz5fYgGCiJYxmS+wt6ziSvqvjzv7nASdSrGnd6KzpqJ8Pz7c2fEiYwmymPerP9YgIsqrBqDRC03fmu0jBFXOmTWc5GQAihGt6BVEEQY6s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779372568; c=relaxed/simple; bh=zVWai+7lGIvjl6SkZBpll6gJb+jxqobnMbSWMceYjNA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=O+2+3heee4f8JUoR5+bBwE+P4hZZPP9M9vYhFHeHMnaEnygx9vkEy+f58F1QKUxsSMnmDnzMIv7p4Nu4UYnW7sI383XI/2PQsqlqFb+Z14aa87xPYWwpDPX1GSseDaNBD/kz1f46tD6zZshNaQ377GV/8QURB4BpDACxO3HilTg= 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=D2F9Qjx4; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=YH+8Duvj; 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="D2F9Qjx4"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="YH+8Duvj" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1779372566; 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: in-reply-to:in-reply-to:references:references; bh=E82Z22wc78DWFtKs22Dwf10Uc2AV6EGoZcG/joqub6E=; b=D2F9Qjx4As0Kd7tdR5gdadhm62D3s3nE3IYr5kzj+w9OQNkCi1x9j0ehbj8Bg9R+4EFRIW WJwPQ/RSh14TaRafYwLzPYvIdkz1RmJ2iYC8OyyU4EtamK20/+p3y+jkC9AVaxvv0TKQmW AGQgVniCZ+rXhah4VYRyXsaOcP/oSnM= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-457-brGlRBdaPRa8LCjIR4ccRA-1; Thu, 21 May 2026 10:09:19 -0400 X-MC-Unique: brGlRBdaPRa8LCjIR4ccRA-1 X-Mimecast-MFC-AGG-ID: brGlRBdaPRa8LCjIR4ccRA_1779372558 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-48fd233d1e2so56956855e9.1 for ; Thu, 21 May 2026 07:09:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1779372558; x=1779977358; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=E82Z22wc78DWFtKs22Dwf10Uc2AV6EGoZcG/joqub6E=; b=YH+8Duvj1msV6hhhX+SZOM3fGFjQGBB1027F/3PwdMKbLabRuFnH4b/LL0cMEl4vxe JAfBeotjRVtOuAlVzaRDLXVSOFqch4lrDDc0keoU1SV8t1t+ncJfeCAicG9eoo1SvudY dXGUfgxlu/dy35c0kPprXr4fKkdHteg8xUezUGfC3vqef2QtDK+iFKs25vgefh4NwHje I2TALCb0jnsfFBsXfN/epwcE/5cCBBppRx2lL384t9rBpS/MzeymHF+TIolmiUGtOY8K MCOzHpz1zlbE4G21yUFr9HC8AYEC4vlZMdUzFx915O1+7XpfWXUc6AZHfA0QtH9JZI1O 1GlA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1779372558; x=1779977358; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=E82Z22wc78DWFtKs22Dwf10Uc2AV6EGoZcG/joqub6E=; b=D8IOAqXJqGKOXPWwJUUBtQln2LRsR/Vg+Ayat+k5GKIqxix1atrMbqq6vzPKHelBMG VmBQUGHbUyRsIV+tFUszRObj7oxo3drxrsll9AZ6lc0U6wPlbzLgSefNwhdC6lapeETG XyQEdgikPEiptPd9H5SYIjSwkIbXVGidaap55WJ6URpU/RNXocXEBF+6ilICfvOvefvE /nLYl95H8axMoNjHWwbvDe0F3HLPQwyYobWyHDKDFZW+LkHKSHl+wjzvqiUNytU7Z5r6 BHQnhGphfggASkcsc9m4jGe/Cter7QRSXimPSUOSfGdfX6w3Bsd2ZZubPK7yFMz6RwTy 94Wg== X-Gm-Message-State: AOJu0Yzdph32SqC0w0ff7nD0GJA8/HbuQtNxuCxoqEtrMfIGG3oHkxHY LFi2wXHa32M1zzwU6QGZbAoDyN+mqkiRQtrAcXntHuq4m3E1oX0UeUSLxelatW8DcUr/MP+tUXo +4/7huHoq0pA8XR4wTwDK9Bi/jiISh3e8vAF+2HaKtI9lXCHrJXWj5ZE1N1QR3m52ZbeT9b66vI ed7mvH2ZAbj6E9IVbC4DAF+ody+ETHdu8eae2hOblv5Ow= X-Gm-Gg: Acq92OFzT8AxK0Qqo5FO+LxO5FqgLKQLY4yPxZpH6sIc5KirtTJ1ZkJ01LlcxCSEljG pE27AQsZDKM4bdlIcU2L/rvhZHOkv578PFY1Ko4+suFn12LmJiR3UwDPrVKjmrneKXFPH9Q9pKi 4j+jLg5Jers54S0YxPIfCLBujk1MQCa/6l9bB9B0Vc/2c4hSMzhaGjHFZfwI2zm+P3A81LuCpC3 EsOtu9C1JzSrrWS8XQ5WNG4rWb56jiPGfaAfBD9nVeWfJq1jqzBo8bUkXECS95kgQnF+gKJQtXv 5Yn9UmkA5gS5PZj2oK+KAaZDKWL0owEXNNZlQ95bc0Y8gRSFx+6X5MH+K7RQn6YaGvS+WBLuHQ4 +K0LNeGAF5MJeeK8Ef03Gl4d4Yrf2vkEUykKvNXmBqfTeuR/HmepCDw== X-Received: by 2002:a05:600c:4e92:b0:490:3b84:c106 with SMTP id 5b1f17b1804b1-4903b84c8ffmr34030505e9.26.1779372557931; Thu, 21 May 2026 07:09:17 -0700 (PDT) X-Received: by 2002:a05:600c:4e92:b0:490:3b84:c106 with SMTP id 5b1f17b1804b1-4903b84c8ffmr34029025e9.26.1779372557076; Thu, 21 May 2026 07:09:17 -0700 (PDT) Received: from redhat.com (IGLD-80-230-25-45.inter.net.il. [80.230.25.45]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4903ad2ee77sm25394465e9.0.2026.05.21.07.09.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 May 2026 07:09:16 -0700 (PDT) Date: Thu, 21 May 2026 10:09:11 -0400 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: "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 , 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 Subject: Re: [PATCH v8 00/37] mm/virtio: skip redundant zeroing of host-zeroed pages Message-ID: <20260521100313-mutt-send-email-mst@kernel.org> References: 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: On Wed, May 20, 2026 at 06:20:13PM -0400, Michael S. Tsirkin wrote: > When a guest reports free pages to the hypervisor via virtio-balloon's > free page reporting, the host typically zeros those pages when reclaiming > their backing memory (e.g., via MADV_DONTNEED on anonymous mappings). > When the guest later reallocates those pages, the kernel zeros them > again, redundantly. FYI Sashiko reported a couple of issues. Mostly false positives but I tweaked commit log to make it clearer. But also a couple of real issues. So far I have this diff on top: ---> Changes from v8 to v9 candidate (code only): 1. mm/mempolicy.c (patch 1: mm: mempolicy: fix interleave index calculation) Combine vm_pgoff and VMA offset into a single expression before shifting, fixing carry loss for file-backed VMAs with unaligned vm_pgoff. 2. mm/memory-failure.c (patch 2: mm: memory-failure: serialize TestSetPageHWPoison with zone->lock) Wrap ClearPageHWPoison in retry path with zone->lock too. 3. mm/huge_memory.c (patch 19: mm: use __GFP_ZERO in vma_alloc_anon_folio_pmd) Fix stale comment: "folio_zero_user writes" -> "page zeroing". 4. mm/page_reporting.c (patch 4: mm: page_reporting: allow driver to set batch capacity) Drop rounddown_pow_of_two: compiler cannot optimize division by runtime variable anyway, and rounding halves batch size for non-power-of-2 capacity values. Commit log improvements (no code change): - Patch 1: rewritten to explain new single-expression formula (fixes patch 1) - Patch 2: mention ClearPageHWPoison in retry path (fixes patch 2) - Patch 4: drop "rounded down to a power of 2" (fixes patch 4) - Patch 10: "stub" wording simplified (fixes patch 10) - Patch 22: note PG_zeroed hint loss is harmless (fixes patch 22) - Patch 23: add PowerPC note (fixes patch 23) - Patch 28: explain DEVICE_INIT_ON_INFLATE is a follow-up (fixes patch 28) - Patch 29: explain flush over-reporting is by design (fixes patch 29) - Patch 33: note __SetPageZeroed is safe on frozen pages (fixes patch 33) - Patch 36: note __SetPageZeroed is safe on balloon-owned pages (fixes patch 36) --- diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 9845c920c29c..4978d34532ea 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1358,7 +1358,7 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma, /* * The memory barrier inside __folio_mark_uptodate makes sure that - * folio_zero_user writes become visible before the set_pmd_at() + * page zeroing becomes visible before the set_pmd_at() * write. */ __folio_mark_uptodate(folio); diff --git a/mm/memory-failure.c b/mm/memory-failure.c index a6b61172dd13..d106f2c135c7 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -2426,7 +2426,9 @@ int memory_failure(unsigned long pfn, int flags) } else { /* We lost the race, try again */ if (retry) { + spin_lock_irqsave(&zone->lock, mf_flags); ClearPageHWPoison(p); + spin_unlock_irqrestore(&zone->lock, mf_flags); retry = false; goto try_again; } diff --git a/mm/mempolicy.c b/mm/mempolicy.c index ea3043e0075b..f573ff32e94d 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2048,9 +2048,9 @@ struct mempolicy *get_vma_policy(struct vm_area_struct *vma, pol = get_task_policy(current); if (pol->mode == MPOL_INTERLEAVE || pol->mode == MPOL_WEIGHTED_INTERLEAVE) { - *ilx += vma->vm_pgoff >> order; - *ilx += (addr >> (PAGE_SHIFT + order)) - - (vma->vm_start >> (PAGE_SHIFT + order)); + *ilx += (vma->vm_pgoff + + (addr >> PAGE_SHIFT) - + (vma->vm_start >> PAGE_SHIFT)) >> order; } return pol; } diff --git a/mm/page_reporting.c b/mm/page_reporting.c index 8b278a494ea5..3f584f538c68 100644 --- a/mm/page_reporting.c +++ b/mm/page_reporting.c @@ -443,9 +443,6 @@ int page_reporting_register(struct page_reporting_dev_info *prdev) if (!prdev->capacity || prdev->capacity > PAGE_REPORTING_CAPACITY) prdev->capacity = PAGE_REPORTING_CAPACITY; - /* Power of 2 so division by capacity in the budget calc is cheap */ - prdev->capacity = rounddown_pow_of_two(prdev->capacity); - /* initialize state and work structures */ atomic_set(&prdev->state, PAGE_REPORTING_IDLE); INIT_DELAYED_WORK(&prdev->work, &page_reporting_process);