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 919F1D39000 for ; Wed, 14 Jan 2026 18:01:18 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 05C456B0088; Wed, 14 Jan 2026 13:01:18 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 033CC6B0089; Wed, 14 Jan 2026 13:01:17 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E9F856B008A; Wed, 14 Jan 2026 13:01:17 -0500 (EST) 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 D71BC6B0088 for ; Wed, 14 Jan 2026 13:01:17 -0500 (EST) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 92BB516059E for ; Wed, 14 Jan 2026 18:01:17 +0000 (UTC) X-FDA: 84331336194.17.A0C31AF Received: from mail-qt1-f181.google.com (mail-qt1-f181.google.com [209.85.160.181]) by imf22.hostedemail.com (Postfix) with ESMTP id 6AF57C0018 for ; Wed, 14 Jan 2026 18:01:15 +0000 (UTC) Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=mN+uJ7wi; spf=pass (imf22.hostedemail.com: domain of surenb@google.com designates 209.85.160.181 as permitted sender) smtp.mailfrom=surenb@google.com; dmarc=pass (policy=reject) header.from=google.com; arc=pass ("google.com:s=arc-20240605:i=1") ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1768413675; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=KDTsqchLttwh0cFXuiS3EpXCzVEnKRStuaHR3bDL9sU=; b=r2eRSsOPiXjYfiDaqSP+KQVNfObB9dYBhe4flda2kRKaJF/T6/BAnk0TDpktoKkO0LcRNp FAcVRt9zGv9P4N030z0o9MADwU5OPhfxKCAI/J4K0mpEaSEUflhl8Zm76msx1V5WZxNSrp 51lr1Wq/RmhmabMhMBYj/zm3YB/q8Nw= ARC-Authentication-Results: i=2; imf22.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b=mN+uJ7wi; spf=pass (imf22.hostedemail.com: domain of surenb@google.com designates 209.85.160.181 as permitted sender) smtp.mailfrom=surenb@google.com; dmarc=pass (policy=reject) header.from=google.com; arc=pass ("google.com:s=arc-20240605:i=1") ARC-Seal: i=2; s=arc-20220608; d=hostedemail.com; t=1768413675; a=rsa-sha256; cv=pass; b=5D9Ga3AIV7VGrtmQJvGrdzp+69ZYovIpgZWBpQLZXYSwLy9lcPCxDsCRdjJ/+jWg/S433H RSIf8ztH2TVbPI0AGP2XNoKWaLbUXfdUv7TRvivQRUljR6CRFRFLij+qBeaquGRU/4Wdsl pfADS+QP37JVZSiWNNKsEX2bhYIUUpc= Received: by mail-qt1-f181.google.com with SMTP id d75a77b69052e-5014acad6f2so6261cf.1 for ; Wed, 14 Jan 2026 10:01:15 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1768413674; cv=none; d=google.com; s=arc-20240605; b=H+5ipuY2KzcY9mfBfYzWV8I2jVCHWW8mjPDKETzEsyExeQfyG/l7RB26oeBoY5uJB3 E8fPptt6tx+ejoQFEd402doAUePAVM7P+VBRxv872MNopePrraI3wW+YBUd66uvgoXQl Q/ssdYvo24VAqKBIYzUWPbCUa9QPW3U23S6L17LLCNHPaE6OuxfTehpwo7SLBaQEhPcs 8VFXzFx049kxpkKPNsNt3Pr089mzLGooQ8nD75bURRWf54IC7kHCt+mVP5+oh5qq6CAd uAtTqDbRNi5KoHPqVLwkB70nqCjpCcq/Y375NFiQ2uT77LscGYik0FKBmGAsoLlgU0dN Rv2Q== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20240605; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:dkim-signature; bh=KDTsqchLttwh0cFXuiS3EpXCzVEnKRStuaHR3bDL9sU=; fh=6eQVREuS/ju3xW0nTne3uMCGWCedKLESYcaBCOa9EgE=; b=dlwY3MiDJyKh6jbMmWBP1H87s0n2ULUOwRF0ga/7VtbsrWJ3rHWfMt57ZfCNS+VDIq roxFHNDEoTUNpXhzUKLAYDDgofWxNGinCJkJ87o9TGdVx/5GAZZJb766yqAErW+55FSX RUdSYhVReRm/zu8B6csrF2q4CTIQSdJEmVkqA6l2ThMx/hQ45XDCQUCC2WOetFbPy4W+ QnRP8y6v0I3Cl5U/e+ynvsFTKYTM0TDRluKA7sjxd7I+em/UL4KF3MX0ct8A6D1sjJdq /JGlfKFmgCYbG38HdeBO9B3xWZhr4apS2lsyq8MSK2wROREd015LR6Wq++v9CzUkmADv bYZg==; darn=kvack.org ARC-Authentication-Results: i=1; mx.google.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1768413674; x=1769018474; darn=kvack.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=KDTsqchLttwh0cFXuiS3EpXCzVEnKRStuaHR3bDL9sU=; b=mN+uJ7wi2aNDh8fWGY3bCBGPFdQgdZy+aA0KCHKSZvJL1FQxgUrd3lCbJs3LJ39Pyp HR6+L3fZ221Iwj4/JABIeqJRFuUi13ZV3ohqG8TWD52XVe3+r2G9I+4BrHm63CRbqMJu 3lkV0UgL5GNQ8PY0j0eJPID/ZlXJC3z1opCTdQyFyXmGuzP7nk/ckbHksuW6iZeKVQij PVioGAT96JHNm/98J5qCFbFIkmbaJy4gbQosWdD+u92Vi4ViLjXkr3sYqoyYNABi497U iJ5tEAxszvx84lx89c7IomqeYsj0+NDddSGQ7O56g90DKkkSGPwcSLS4ZywnS+oI7qZK ZtkQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1768413674; x=1769018474; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=KDTsqchLttwh0cFXuiS3EpXCzVEnKRStuaHR3bDL9sU=; b=UmyfkZhxPRIMJeq04s2jJKXuRQa0Sa56bCoG5OdeXh/1Hb1ULZ8nYLL6GerSFIAkLV 8Rs93a5Fdzd4YvPwiu0KV70K2KubigncFysJEtjd2/vQle0LeaXpaV0bBH3U7mmB3zpt rwt/EtTijBtR1/XVVt6M0sQPnJBlkBpwtkSP7vo3mZkDzluuJOo+xyb66Aoeec+5Tuar O+Z9cxD13RwdjcynlG0771ggK9KWd0hETWFzk9K1sXELoFaqMDDta9LhLKwcC3XP2lyk og06Gp0tIJFqm4iqXpBRwxV6mwDwFVcBTkWRdo4lkBVr/4KCoggnqNEqsqSZSogB2qPN kmzw== X-Forwarded-Encrypted: i=1; AJvYcCV4eEoUd1LJx23YhwqbsfZFKDS0uUx0qWpLLV/MozfW1lvPzX/AZFr7XNB6zF7JzjsroOf2Kmhemw==@kvack.org X-Gm-Message-State: AOJu0YyGvfyei/Ctnwp/RPUUII/kiT+Sd/mvbQBvOFd0sPp16+LxfLIS v9gi4Sbe1xvqG2/Pr6MFisxt6raY57xJvuGxa9p5p3xm77kuFHi+iT4WblcEc7uC0lOJWHfmnB0 rzWqa3jGFhKHZJIHGQeyx4Q/F5D3vLLN+NMyYgb9I X-Gm-Gg: AY/fxX7Bm8NvMsjNsxFBhKmi4aCUu4ewknV/Jro57nbKHnw2bPse1UW5Xkfnr2CJTeK txTaAwup/XwTpzRNT8SFif7QQf9t39B0MFffmV3ruYR9sihFYrclvFeivXSF1NTxx9gr2eS8erw fjQ49bPfG6ImFHjpkg2DKLNv/sUC72glWFjXto6+GsZejkfa5mr5bIRhFwjb6S9gH4FBFdYf9n7 SWnJrnn/EJujrahJnbR9RQJ2gDfD6uuNv0bU2DigCTxlllz5oYWyMY4KzBIsNZzcG487WpNvIGx uuVsWocry+OniGMGXVzXLfEAGw== X-Received: by 2002:a05:622a:190b:b0:4ed:8103:8c37 with SMTP id d75a77b69052e-50148257b6fmr15030931cf.12.1768413673859; Wed, 14 Jan 2026 10:01:13 -0800 (PST) MIME-Version: 1.0 References: <9b5a438237e4ea3b19a986a4f8fddb8848cba54a.1767711638.git.lorenzo.stoakes@oracle.com> <2808d8d8-e772-4210-ada4-2b39d30c7029@lucifer.local> In-Reply-To: <2808d8d8-e772-4210-ada4-2b39d30c7029@lucifer.local> From: Suren Baghdasaryan Date: Wed, 14 Jan 2026 10:01:02 -0800 X-Gm-Features: AZwV_QhtRRztUvUhMt6-Y_uG10BKbcB2fxnrgvhz6T6kogsSj3PTiIy7Dr58sro Message-ID: Subject: Re: [PATCH v2 3/8] mm/rmap: remove unnecessary root lock dance in anon_vma clone, unmap To: Lorenzo Stoakes Cc: Andrew Morton , "Liam R . Howlett" , Vlastimil Babka , Shakeel Butt , David Hildenbrand , Rik van Riel , Harry Yoo , Jann Horn , Mike Rapoport , Michal Hocko , Pedro Falcato , Chris Li , Barry Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 6AF57C0018 X-Stat-Signature: 5aknmhm59t1un941xz7hbm1cadznxwp5 X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1768413675-923189 X-HE-Meta: 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 JpCuBGlX fExTwt7tolh2EuvPBnvXALMkocGoVWfFaZTUqiWoRieLOB+7iiFhj8JymagIHl0TGoYy+y6xL8ygjPaC/pis4/oBPV4Myr86ZfwxT5wjxRklFP+PdKLEf3/U941XEWKd+onNVKJW1WLcDXBPjlUcrq49yF95Q4japbaj/pDLnExKX2yODy1wwt4GzyAy1G128Jeo4fP2kuC913cR59Di4OufwonhivyQJGTz5Et5mKuc7Yimn7e45YCGvWvzpTGsbsolrSpMvof6qWJXIgf2aD5GfIr6AO+gxN+IqejtladHFzM08GCvMFdFBzg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jan 14, 2026 at 9:54=E2=80=AFAM Lorenzo Stoakes wrote: > > On Wed, Jan 14, 2026 at 08:55:58AM -0800, Suren Baghdasaryan wrote: > > On Tue, Jan 6, 2026 at 7:04=E2=80=AFAM Lorenzo Stoakes > > wrote: > > > > > > The root anon_vma of all anon_vma's linked to a VMA must by definitio= n be > > > the same - a VMA and all of its descendants/ancestors must exist in t= he > > > same CoW chain. > > > > > > Commit bb4aa39676f7 ("mm: avoid repeated anon_vma lock/unlock sequenc= es in > > > anon_vma_clone()") introduced paranoid checking of the root anon_vma > > > remaining the same throughout all AVC's in 2011. > > > > > > I think 15 years later we can safely assume that this is always the c= ase. > > > > > > Additionally, since unfaulted VMAs being cloned from or unlinked are > > > no-op's, we can simply lock the anon_vma's associated with this rathe= r than > > > doing any specific dance around this. > > > > > > This removes unnecessary checks and makes it clear that the root anon= _vma > > > is shared between all anon_vma's in a given VMA's anon_vma_chain. > > > > > > Signed-off-by: Lorenzo Stoakes > > > --- > > > mm/rmap.c | 51 +++++++++++++++------------------------------------ > > > 1 file changed, 15 insertions(+), 36 deletions(-) > > > > > > diff --git a/mm/rmap.c b/mm/rmap.c > > > index de2cbe860566..6ac42671bedd 100644 > > > --- a/mm/rmap.c > > > +++ b/mm/rmap.c > > > @@ -232,32 +232,6 @@ int __anon_vma_prepare(struct vm_area_struct *vm= a) > > > return -ENOMEM; > > > } > > > > > > -/* > > > - * This is a useful helper function for locking the anon_vma root as > > > - * we traverse the vma->anon_vma_chain, looping over anon_vma's that > > > - * have the same vma. > > > - * > > > - * Such anon_vma's should have the same root, so you'd expect to see > > > - * just a single mutex_lock for the whole traversal. > > > - */ > > > -static inline struct anon_vma *lock_anon_vma_root(struct anon_vma *r= oot, struct anon_vma *anon_vma) > > > -{ > > > - struct anon_vma *new_root =3D anon_vma->root; > > > - if (new_root !=3D root) { > > > - if (WARN_ON_ONCE(root)) > > > - up_write(&root->rwsem); > > > - root =3D new_root; > > > - down_write(&root->rwsem); > > > - } > > > - return root; > > > -} > > > - > > > -static inline void unlock_anon_vma_root(struct anon_vma *root) > > > -{ > > > - if (root) > > > - up_write(&root->rwsem); > > > -} > > > - > > > static void check_anon_vma_clone(struct vm_area_struct *dst, > > > struct vm_area_struct *src) > > > { > > > @@ -310,26 +284,28 @@ static void cleanup_partial_anon_vmas(struct vm= _area_struct *vma); > > > int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct= *src) > > > { > > > struct anon_vma_chain *avc, *pavc; > > > - struct anon_vma *root =3D NULL; > > > > > > check_anon_vma_clone(dst, src); > > > > > > if (!src->anon_vma) > > > return 0; > > > > > > + check_anon_vma_clone(dst, src); > > > > check_anon_vma_clone() was already called 4 lines above. I'm guessing > > this was accidentally carried over from the previous version? > > > > Yeah I don't know why this is here, in the tree it isn't, maybe Andrew no= ticed > and elided? :) I noticed when reviewing later patches that you remove this extra call in one of them. That's why the current tree is fine. > > But yeah the check above is correct so current in-tree state is correct. > > Thanks, Lorenzo