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 74856FB5173 for ; Tue, 7 Apr 2026 00:50:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A39116B0088; Mon, 6 Apr 2026 20:50:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9E9EB6B0089; Mon, 6 Apr 2026 20:50:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8D8616B008A; Mon, 6 Apr 2026 20:50:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 7C24F6B0088 for ; Mon, 6 Apr 2026 20:50:35 -0400 (EDT) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 03F49598A5 for ; Tue, 7 Apr 2026 00:50:34 +0000 (UTC) X-FDA: 84629929230.17.FB52FE9 Received: from crocodile.elm.relay.mailchannels.net (crocodile.elm.relay.mailchannels.net [23.83.212.45]) by imf29.hostedemail.com (Postfix) with ESMTP id 680B312000E for ; Tue, 7 Apr 2026 00:50:32 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=stgolabs.net header.s=dreamhost header.b=mv1Cg4rr; dmarc=none; arc=pass ("mailchannels.net:s=arc-2022:i=1"); spf=softfail (imf29.hostedemail.com: 23.83.212.45 is neither permitted nor denied by domain of dave@stgolabs.net) smtp.mailfrom=dave@stgolabs.net ARC-Seal: i=2; s=arc-20220608; d=hostedemail.com; t=1775523032; a=rsa-sha256; cv=pass; b=8e8llArCd9fhB6AnJK3DfnvUw0equwJePniKgCAzIyHftOSbSZ9DabqkmflGxsMHCj7Dyy iJmMptIwYAZsx82rxNT134g7vgFF8DulSnUhp41L8byzAbiOXjaZPIwSxWfQ2pFD88alZu AHG9hvahvQFAY1zQ+SK6wfxuO99NM5U= ARC-Authentication-Results: i=2; imf29.hostedemail.com; dkim=pass header.d=stgolabs.net header.s=dreamhost header.b=mv1Cg4rr; dmarc=none; arc=pass ("mailchannels.net:s=arc-2022:i=1"); spf=softfail (imf29.hostedemail.com: 23.83.212.45 is neither permitted nor denied by domain of dave@stgolabs.net) smtp.mailfrom=dave@stgolabs.net ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1775523032; 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=cMwxCUdDzcCtqZxPCuLtLzFRvDztipo2RCcHqTcTHXY=; b=244WdNlPy+8os2E5LEmg3ELuIy52FF9YLdDZKflQ8Nc4HrDSmw3Yy66cZphXdAfbeQ4P0Z 0loU1Z1DH5CYz6nn9UYH/+wHuScFhuJRGjdcB5cCEn+JunqSj/RT68qoqiJbT4fslyArCK Gvv2b6r2XxIOzoHCJsDNMldBsfC9Gak= X-Sender-Id: dreamhost|x-authsender|dave@stgolabs.net Received: from relay.mailchannels.net (localhost [127.0.0.1]) by relay.mailchannels.net (Postfix) with ESMTP id C60C37E2FB9; Tue, 07 Apr 2026 00:50:30 +0000 (UTC) Received: from pdx1-sub0-mail-a247.dreamhost.com (trex-green-6.trex.outbound.svc.cluster.local [100.118.167.109]) (Authenticated sender: dreamhost) by relay.mailchannels.net (Postfix) with ESMTPA id 5656D7E2FE6; Tue, 07 Apr 2026 00:50:30 +0000 (UTC) ARC-Seal: i=1; a=rsa-sha256; d=mailchannels.net; s=arc-2022; cv=none; t=1775523030; b=PQ8g6XBGhZ3w8GyAzZxmtZDDF8PRma6cYXOwYdQ1IXTE60d7reRM30s5WLPy+SyoWuoEA2 OXktNd2OKP0/azrdNfbZYnbijPeqA53TMuG/6XKtLSmWyyAuz4z97WE64KamvHOC0S0g/k Y+NzGdsHa/Tp8l85MzMIEOVuoL5xJhEBgJUCyC7K4aN2Q+3oCw4O95y2ILtL+Y6ETuMZl5 ETgMcOhLk+ebgdiQk9wxu8szouKShR7XegUHkmPMnKwazj+/zm1GuXfCyNqTabOI60zMxI lju02TVt2n0OGLAWeDqTavsgxa7t42KLuuDhjsO5X6V2Rn5nXstkw+wLSMRlfQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=mailchannels.net; s=arc-2022; t=1775523030; 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:dkim-signature; bh=cMwxCUdDzcCtqZxPCuLtLzFRvDztipo2RCcHqTcTHXY=; b=A7QBoKdFgJgD6nuljAjde7LQCjT6y/o4QFt+4Qo7FUmaUcjblJOBetMcWpO8lMJZfB7Wi+ ENkAYNmYhWozJfRMlftCEUG6SLH0lxljHws/KbGvlG0t8+xCWaz7VmWUDEhQ0pmYejZWiQ hTEoOTrmHFoDgpcchs4Vh6UaaLgycCPFOX5xSiC0DtGeK+c3HW43RloeCfJfIfbZoR7j4W +mqACVNEw2lkTzGDWUlH2JdxU35T7mPhbjWoQe6phJCwbmpsuVNJqOr3tjVeDPNZ4SHdzp FroUHCdnJ96iC8pvCOPbtf/W1b+O+ZB4rdhFEomffKssda8htW5HgcjEm3f8jw== ARC-Authentication-Results: i=1; rspamd-7d86dcc447-zkbxw; auth=pass smtp.auth=dreamhost smtp.mailfrom=dave@stgolabs.net X-Sender-Id: dreamhost|x-authsender|dave@stgolabs.net X-MC-Relay: Neutral X-MailChannels-SenderId: dreamhost|x-authsender|dave@stgolabs.net X-MailChannels-Auth-Id: dreamhost X-Cooperative-Relation: 7a2bd04419e8d27e_1775523030651_2650626807 X-MC-Loop-Signature: 1775523030651:4205056266 X-MC-Ingress-Time: 1775523030651 Received: from pdx1-sub0-mail-a247.dreamhost.com (pop.dreamhost.com [64.90.62.162]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384) by 100.118.167.109 (trex/7.1.5); Tue, 07 Apr 2026 00:50:30 +0000 Received: from offworld (unknown [76.167.199.67]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: dave@stgolabs.net) by pdx1-sub0-mail-a247.dreamhost.com (Postfix) with ESMTPSA id 4fqSKd484Wz106F; Mon, 6 Apr 2026 17:50:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=stgolabs.net; s=dreamhost; t=1775523030; bh=cMwxCUdDzcCtqZxPCuLtLzFRvDztipo2RCcHqTcTHXY=; h=Date:From:To:Cc:Subject:Content-Type; b=mv1Cg4rr3UA6eaGve5YgvG77w4ObAXvFsTim2FNTd9d8Gbzgy4wB6+r6kLbfSXn8Y EcKmcQvmIANOGQl2dekmu76q4jfs3F9s+Ad99W/odWYAafHnaKGlULG65Lm5BEdGjw UHB0iLDE86uWB+iKmySfhCCHC6RyptXweYrd1MQ7x6NtnqsW1kRnbaAT3sVtBOLaWv XuTF53MdQZj5JigOcH4K4GAnKc5m3WaBhxvIy8zqG5AHZJzPhdsdpvLX0Zpe3MJ/YF 9PJUAhRo3ph6CNQv/vu1CtLqX4CAYiJAQYisog9w553GsEQdeHF0+CqQKP7bh897vH fQUVajMRWapAA== Date: Mon, 6 Apr 2026 17:50:26 -0700 From: Davidlohr Bueso To: Pedro Falcato Cc: Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , David Hildenbrand , Dev Jain , Luke Yang , jhladky@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 2/2] mm/mprotect: special-case small folios when applying write permissions Message-ID: <20260407005026.ytf7ed4bk2ljyflx@offworld> Mail-Followup-To: Pedro Falcato , Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , David Hildenbrand , Dev Jain , Luke Yang , jhladky@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260402141628.3367596-1-pfalcato@suse.de> <20260402141628.3367596-3-pfalcato@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20260402141628.3367596-3-pfalcato@suse.de> User-Agent: NeoMutt/20220429 X-Stat-Signature: yecaahhkcwt9ssmmtdez7icskhfyqe4n X-Rspamd-Queue-Id: 680B312000E X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1775523032-157557 X-HE-Meta: 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 7QYhWJPn 5NKmZy+9Q6vxjQ8oAHCT7cmBghnpXrWHKYlK+C0XC8qJaw6SNHCY1OesRvQM3N3rTEVczwypNpPuSjXpZE/8Aru/zHxiHl13Q/vA81HAEGE84+OHKONbrfnzfvpmciPjEnkG64zm+7q2m3nsvP0Zb9bN8t5SXeDU5pSV2MbLQPc8Xlyaj/FPVwEdymHH5bTh87R0HMF/KO7sq+q931HmWeHPL4tl5yhK0CQINxDl60qBcdDuFoS+2/n3Zuvj96V8OjglTTkeN6JkdlLR5D4VjrSfkWMox4XamjiaDUeeE+gNyySwlTdfrmO5S/+xtR7f8Fyup Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 02 Apr 2026, Pedro Falcato wrote: >@@ -334,34 +371,20 @@ static long change_pte_range(struct mmu_gather *tlb, > > nr_ptes = mprotect_folio_pte_batch(folio, pte, oldpte, max_nr_ptes, flags); > >- oldpte = modify_prot_start_ptes(vma, addr, pte, nr_ptes); >- ptent = pte_modify(oldpte, newprot); >- >- if (uffd_wp) >- ptent = pte_mkuffd_wp(ptent); >- else if (uffd_wp_resolve) >- ptent = pte_clear_uffd_wp(ptent); >- > /* >- * In some writable, shared mappings, we might want >- * to catch actual write access -- see >- * vma_wants_writenotify(). >- * >- * In all writable, private mappings, we have to >- * properly handle COW. >- * >- * In both cases, we can sometimes still change PTEs >- * writable and avoid the write-fault handler, for >- * example, if a PTE is already dirty and no other >- * COW or special handling is required. >+ * Optimize for the small-folio common case by >+ * special-casing it here. Compiler constant propagation >+ * plus copious amounts of __always_inline does wonders. > */ >- if ((cp_flags & MM_CP_TRY_CHANGE_WRITABLE) && >- !pte_write(ptent)) >- set_write_prot_commit_flush_ptes(vma, folio, page, >- addr, pte, oldpte, ptent, nr_ptes, tlb); >- else >- prot_commit_flush_ptes(vma, addr, pte, oldpte, ptent, >- nr_ptes, /* idx = */ 0, /* set_write = */ false, tlb); >+ if (likely(nr_ptes == 1)) { Are there any numbers for this optimization? While I am all for optimizing the common case, it seems unfair to penalize the uncommon one here. Why is nr_ptes > 1 such an exotic use case (specially today)? ie: How does this change affect the program in b9bf6c2872c ("mm: refactor MM_CP_PROT_NUMA skipping case into new function"), which is a series for optimizing large folio cases. Thanks, Davidlohr >+ change_present_ptes(tlb, vma, addr, pte, 1, >+ end, newprot, folio, page, cp_flags); >+ } else { >+ change_present_ptes(tlb, vma, addr, pte, >+ nr_ptes, end, newprot, folio, page, >+ cp_flags); >+ } >+ > pages += nr_ptes; > } else if (pte_none(oldpte)) { > /* >-- >2.53.0 > >