From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D6D8CCD8C9F for ; Mon, 8 Jun 2026 12:32:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4522E6B0005; Mon, 8 Jun 2026 08:32:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 42A486B0088; Mon, 8 Jun 2026 08:32:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 366F96B0092; Mon, 8 Jun 2026 08:32:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 250F86B0005 for ; Mon, 8 Jun 2026 08:32:36 -0400 (EDT) Received: from smtpin15.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id BF5AD1C2CA1 for ; Mon, 8 Jun 2026 12:32:35 +0000 (UTC) X-FDA: 84856683870.15.09D8C18 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf01.hostedemail.com (Postfix) with ESMTP id 113CF4000C for ; Mon, 8 Jun 2026 12:32:33 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="BokOJ/53"; spf=pass (imf01.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1780921954; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=0S/mGlm2XVUNmf88aZNmWlasF/PmDk0YOd5RS53eddI=; b=lGI4Z7JartAMjwC5VDv7ZVXdYLL4NEPfrpVBjzH3lgMNIh0ccKRkQtwkOZP5zJ8/IR5ngI HNURsKU+fV3HWOSTiNWjdHcq9WxH62nKYEy0aAXoYkzZZAVRaKeStUp8EiBVdu7DaRNR0w 9xS0AiYeXfe6J/FhcwIKGgwoMYwat+4= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="BokOJ/53"; spf=pass (imf01.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1780921954; b=jDeSRKGqaBsA1/id5nFyqeacJhdaIkvSLzaut3UBwX2igfuV7u4kru3W0wVPddGYWs0YVK AuL1TmYLawKOtkOKN7W1haLPToXt5Or4IPCocFcp+XErp6v8yal47inBT02uuYgc5+Bozj pi87IIJr2l+mdkPPmbquuW35caNFGVY= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 3ABE1434D2; Mon, 8 Jun 2026 12:32:33 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 689F31F00893; Mon, 8 Jun 2026 12:32:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780921953; bh=0S/mGlm2XVUNmf88aZNmWlasF/PmDk0YOd5RS53eddI=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=BokOJ/53zXQSSC08VD4iug5xPluwrLQ0Ns/1S+/wn18UiuwksvNkniq3qN2FiyewF GMuvCqRpVL0AlJs6aH6tV8YnDN6p+tnV36+1VnBfbTg0jLsYa8433FvIyLHiH3L8yt htaAfUxpnK80iRWeE/PmXHjXPd4o8iNJJ3tVHTfoDnfYO85+edAF3UZK+nO5rForZG /e0J1UFqLl49pfl5O5uW9t+z+yty8dCmRSFwYT4x34bo+/LfAw2X0dBGkMs0gnUA5O LsnRz9VdOFvVPpU9ZGJJYEmusi3LUDyWanA4z1E41tVtyd4j0FxP+4OJa44yqGoh7E qNprUiV5urzPg== Date: Mon, 8 Jun 2026 13:32:20 +0100 From: Lorenzo Stoakes To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, "David Hildenbrand (Arm)" , Jason Wang , Xuan Zhuo , Eugenio =?utf-8?B?UMOpcmV6?= , Muchun Song , Oscar Salvador , Andrew Morton , "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 v10 27/37] mm: use __GFP_ZERO in vma_alloc_anon_folio_pmd Message-ID: References: <2ee827fed4765a155d2b56bb0e13d7ee5fc6dce8.1780906288.git.mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2ee827fed4765a155d2b56bb0e13d7ee5fc6dce8.1780906288.git.mst@redhat.com> X-Rspamd-Queue-Id: 113CF4000C X-Stat-Signature: 3yjc784iopask1kzgg1g4943cenb9qon X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1780921953-746287 X-HE-Meta: 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 06UG+75i zY/4dObL6eh14TDlI/uCH53WkF0pmTNc+Cby9MJ01gGU4/EZPw7g+/FcJxIrNDz8xNSEfHCqsPyuu57lfvg/luiONY3Lxg4IZc2BED8wkS8zsu8XM0f/Qv8fBGXmfj1SIQoQigcJQ036o/agr2QKmjib9qknsJBV0TPh9OYP9y9G5afUNElsfIXI76NLQuubVC55mL1PonodQ8bQxXpVkQs0eW0VmchwSqzXV1nb1dwylkyoedsLixW3x1PBQo1pvijrsRUdYEccXpe0jbACKf1Yg/dvjUwrNQOXKM1bFNP4Um1SgHPSuh8VXfDnPAnMYr3uzi44dyhzC2B+i6EmirbjRwKyiIzr0XvcLuvAjKnfjDKHuzzCtXGIca9oBQCKiguhwYvKzFw707cipoTjSgk6oZYxEJBZ1/4cwebTF46TiWrhAPBBiiAtj5+niF04bXJMfvlIVxmlh3pc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jun 08, 2026 at 04:39:18AM -0400, Michael S. Tsirkin wrote: > Convert vma_alloc_anon_folio_pmd() to pass __GFP_ZERO instead of > zeroing at the callsite. post_alloc_hook uses the fault address > passed through vma_alloc_folio for cache-friendly zeroing. > > Note: before this series, replacing folio_zero_user() with > __GFP_ZERO was unsafe on cache-aliasing architectures because > __GFP_ZERO uses clear_page() without a dcache flush. With this > series, it is safe if the caller passes a valid user address > (not USER_ADDR_NONE) to vma_alloc_folio() etc., which delivers > it to post_alloc_hook() for the dcache flush via > folio_zero_user(). It is only unsafe if USER_ADDR_NONE is passed. > > Note: with __GFP_ZERO, the folio is zeroed before > mem_cgroup_charge(). If the charge fails, the zeroing work is > wasted. Previously zeroing was done after a successful charge. > This is inherent to moving zeroing into the allocator. > Charge failures are rare (only at cgroup limits). > > Use folio_put_zeroed() on charge failure so the zeroed hint > propagates to the buddy allocator, avoiding redundant re-zeroing > on the next allocation attempt. Again, is this worth it?... Every bit of code added increases risks of bugs, maintenance burden, etc. let's just not do stuff because we can. > > Signed-off-by: Michael S. Tsirkin > Reviewed-by: Gregory Price > Assisted-by: Claude:claude-opus-4-6 > --- > mm/huge_memory.c | 14 +++----------- > 1 file changed, 3 insertions(+), 11 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index d689e6491ddb..0dec3c717ff2 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1333,7 +1333,7 @@ EXPORT_SYMBOL_GPL(thp_get_unmapped_area); > static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma, > unsigned long addr) > { > - gfp_t gfp = vma_thp_gfp_mask(vma); > + gfp_t gfp = vma_thp_gfp_mask(vma) | __GFP_ZERO; > const int order = HPAGE_PMD_ORDER; > struct folio *folio; > > @@ -1347,7 +1347,7 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma, > > VM_BUG_ON_FOLIO(!folio_test_large(folio), folio); > if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) { > - folio_put(folio); > + folio_put_zeroed(folio); Same comments as previously. > count_vm_event(THP_FAULT_FALLBACK); > count_vm_event(THP_FAULT_FALLBACK_CHARGE); > count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK); > @@ -1356,17 +1356,9 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma, > } > folio_throttle_swaprate(folio, gfp); > > - /* > - * When a folio is not zeroed during allocation (__GFP_ZERO not used) > - * or user folios require special handling, folio_zero_user() is used to > - * make sure that the page corresponding to the faulting address will be > - * hot in the cache after zeroing. > - */ > - if (user_alloc_needs_zeroing()) > - folio_zero_user(folio, addr); > /* > * 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() folio zeroing? > * write. > */ > __folio_mark_uptodate(folio); > -- > MST > Thanks, Lorenzo