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 E9B8ACD8C9D for ; Mon, 8 Jun 2026 12:18:28 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3EF0E6B0088; Mon, 8 Jun 2026 08:18:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 39F956B008A; Mon, 8 Jun 2026 08:18:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2B6B76B008C; Mon, 8 Jun 2026 08:18:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 1B5DF6B0088 for ; Mon, 8 Jun 2026 08:18:28 -0400 (EDT) Received: from smtpin01.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay10.hostedemail.com (Postfix) with ESMTP id B26AFC34EB for ; Mon, 8 Jun 2026 12:18:27 +0000 (UTC) X-FDA: 84856648254.01.09C49AA Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf27.hostedemail.com (Postfix) with ESMTP id 065A94000D for ; Mon, 8 Jun 2026 12:18:25 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="fhx34/wY"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf27.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1780921106; 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=4bq7322kWx6CdkqZCl5t40hKw6vHtvbzE6Il0jH62XQ=; b=GmEBb/tHDBtd0kQWoeULwqrd3JZMVRXfGnQCeFjmmJzCcjFd932SfvVeWTZ++gEaE0uyp3 fFn4jFs6ef6csxgMjWWLFREHJ3e1WS9JAohJiEuZ244NOtykn3sRlGoTF/DOhGt0DXou5g z7Vd32flKdn26cYmJNDwA90bqrnFr0Y= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="fhx34/wY"; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf27.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1780921106; b=G3/y8a8PqpHwp+ukxjBhYBFe0JRu4rosBkX2OGBKkQa1xdIA9WV0vLC+wfs74OtGoBvBKB hOSftcur1EZjLJfkQf9N2QIzgQu68fy8EJgMLhdZcICwNW8cnCJBojFbVfFVJuNprbtArf tTnB8d8fKNF6mUCCLwTTcwh361qHaSY= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 2F2FD42ABC; Mon, 8 Jun 2026 12:18:25 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 544311F00893; Mon, 8 Jun 2026 12:18:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780921105; bh=4bq7322kWx6CdkqZCl5t40hKw6vHtvbzE6Il0jH62XQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=fhx34/wYyi4qTtqk4QuiP7p33JtlGJpEvv3WVDq4OHpVAN/F67imxKA0NQ0PqHEOO ShQSTE81rARoCwQ9cNRunKxJJ84J+2QO2PhgO/o+PyUyavv7Yst3B14CC7xOqqUZGZ M63vkmttzEJG3+GVuoNTTyrYgclFhpFN3cFQhCxmosN3QKE78i6tIT++nSeHN5PKO/ 1qzSKEBjkThQMvqNYdB7dYV/Ar8pPs/LlN7E3nYNn96yANKRBbtcyed3o2rbmtMT3v NVdQXSbpCvQ5WhFx0fz4IKTeueDE8+W+Bi+L0den+inJc3U9pCC/5TBx2D0YYS/yFA CMUS8qxjqs+aQ== Date: Mon, 8 Jun 2026 13:18:12 +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 23/37] mm: page_alloc: skip kernel_init_pages for FPI_ZEROED when safe Message-ID: References: <7de6959a0fb1b255dc9bee2de494f51a6c21e468.1780906288.git.mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7de6959a0fb1b255dc9bee2de494f51a6c21e468.1780906288.git.mst@redhat.com> X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 065A94000D X-Stat-Signature: z1pxx5xpj3s6bar5f5kj7urcyf8jxccj X-HE-Tag: 1780921105-209846 X-HE-Meta: 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 r8ob50Ko knv25e2kxN38AKENzGu7A8MWBKsiWBaHhktXxCVgyccPiTDa08KajEGRwL3SbJ2JVc5PY30T7swOhXdRfVvtW2pnqbkkJZFqwn1vDSXPZ0cMfel3HMNOV4wjfzUy3qu30bbsohWvLJR6nULDEObfVQNm1qcnAlbi23vFeo7owrgmXDj1KqSaJ8RYveDJxu4oOT+JHTNo5OAGhLkDwCQ5SgDLpX1RcP8nSJWNKZiZK0jCIxumQGk4yLN6gs12jGKZt7Ntu3kPi3rzHEKXwkwporCS0nQJQlBGnIR77lzAmedbWtbRIKKqfOIvnQOnvpdZFqEn6ykMEfgsvkquSF8p8N5fMzCoYJJsRu31fSpx7vx8b5OSde3RP/H+QfntDFMP9LSFJCDTNAHLynDfeRU+Gr9/5fw== 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 04:38:46AM -0400, Michael S. Tsirkin wrote: > In __free_pages_prepare(), when FPI_ZEROED is set the page is already > known to be zero. We can skip kernel_init_pages() if page poisoning is > not enabled (because poison would overwrite the zeroes). > > This avoids redundant zeroing work when freeing pages that are already > known to contain all zeros. > > Signed-off-by: Michael S. Tsirkin > Assisted-by: Claude:claude-opus-4-6 > --- > mm/page_alloc.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 008f1a311c40..e3a7c40c769c 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1443,7 +1443,14 @@ __always_inline bool __free_pages_prepare(struct page *page, > if (kasan_has_integrated_init()) > init = false; > } > - if (init) > + /* > + * Skip redundant zeroing when the page is already known-zero > + * (FPI_ZEROED) and page poisoning did not overwrite it. > + * When page_poisoning is enabled, kernel_poison_pages above > + * wrote PAGE_POISON (0xAA), so we must re-zero. > + */ Again, please stop specifying arbitrary hex values in comments, this seems mostly 'describing what we do here'. Maybe drop to just e.g.: /* if poisoned or not zeroed by a virtualised host, zero now. */ or suchlike? > + if (init && !((fpi_flags & FPI_ZEROED) && > + !page_poisoning_enabled_static())) This condition is absolutely horrible, !(X && !Y), you're making life difficult for the readers. 'if not both zeroed and not poisoned' is how that reads logically. Which is hard to understand. De Morgan's law gives us -> !zeroed || posioned How about: if (init && (!(fpi_flags & FPI_ZEROED) || page_poisoning_enabled_static()) Or preferably something like: const bool poisoned = page_poisoning_enabled_static(); const bool vm_host_zeroed = fpi_flags & FPI_ZEROED; ... if (init && (poisoned || !vm_host_zeroed)) ... ? > kernel_init_pages(page, 1 << order); > > /* > -- > MST > Thanks, Lorenzo