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 59AC4C9830E for ; Sun, 27 Sep 2026 22:55:17 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 025466B0088; Sun, 27 Sep 2026 18:55:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F17FF6B008A; Sun, 27 Sep 2026 18:55:15 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E2DC36B008C; Sun, 27 Sep 2026 18:55:15 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id C44E16B0088 for ; Sun, 27 Sep 2026 18:55:15 -0400 (EDT) Received: from smtpin03.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay02.hostedemail.com (Postfix) with ESMTP id AE863120631 for ; Sun, 27 Sep 2026 22:55:13 +0000 (UTC) X-FDA: 85261049706.03.7DA4979 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf01.hostedemail.com (Postfix) with ESMTP id 4960640004 for ; Sun, 27 Sep 2026 22:55:09 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=eIGI0kb8; spf=pass (imf01.hostedemail.com: domain of willy@infradead.org designates 90.155.50.34 as permitted sender) smtp.mailfrom=willy@infradead.org; dmarc=pass (policy=none) header.from=infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1790549712; 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=fonZKBEVnLUi3nmIxkkXaoCZILdYms0d8ZYuqeeaJBg=; b=TL6j4Yfziz1X4zn37elPLSkY3iGybfLhp8L8cjYzS6+x4OJIPBO/KiBOzHuEFNJAr8S0Ov ERNHjtl8d0zqf7eqElAmyphYw7tBR/tgbFGS7Vn4LzvhuiMfu7T1bgDQYSRLQroDqv6sCo OLHbYf1rA+xg8iJtVpeaEmS5I+KsrnQ= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=eIGI0kb8; spf=pass (imf01.hostedemail.com: domain of willy@infradead.org designates 90.155.50.34 as permitted sender) smtp.mailfrom=willy@infradead.org; dmarc=pass (policy=none) header.from=infradead.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1790549712; b=DQWiv3MX7f6TSk442jLF0WRfC5fYSfw+zJkILbKubwMxIwip2GWS+ZHaiRKRMaF9/k0IFf nsyiteHmxN1oveSooAKElOMMXZq5Bi9NDIPfb9YvWbGhQ8fe1kuPpeVLpRi8fQn25FRYG2 O+3Px+/5n0nkNp7HyW7TuvW4ftjfkt8= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=fonZKBEVnLUi3nmIxkkXaoCZILdYms0d8ZYuqeeaJBg=; b=eIGI0kb8JoQ6f59QATnKY4VWTy KlWA18PX6hX10BKhOmxNq0tGi3u1aRfvl4+RCRxnypG+Q3zub+tAGfPLahvJ7UxrqebG6Hw87AV+5 pjJ5wII77N8SG6ISTZur4tDlzHyQJG/AruwRnBvYUL5h5vM1R4LIVih5MQuljHXPOD6svEMX0vt5w fN1uh3q8xkndWOy2mJeEInuuRC2htXs6SWKt9eP27BmPHjB6Elzy1vZxpqCT0Gl7etIkQcBpxUbK4 n8v611VA11zwhLqKPmNANUdBBOafXd7NBkYlngO75KzUN/H3oVubmt74amemlxLWMaFpHJpsXr2/5 Lk6vs5tg==; Received: from willy by casper.infradead.org with local (Exim 4.99.1 #2 (Red Hat Linux)) id 1xAxlt-000000025TY-0cPK; Sun, 27 Sep 2026 22:55:01 +0000 Date: Sun, 27 Sep 2026 23:55:01 +0100 From: Matthew Wilcox To: "Lorenzo Stoakes (ARM)" Cc: Hongru Zhang , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, baohua@kernel.org, surenb@google.com, david@kernel.org, liam@infradead.org, mhocko@suse.com, rppt@kernel.org, shakeel.butt@linux.dev, vbabka@kernel.org, zhaonanzhe@xiaomi.com, linux@armlinux.org.uk, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, linux-arm-kernel@lists.infradead.org, chenhuacai@kernel.org, kernel@xen0n.name, loongarch@lists.linux.dev, maddy@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com, chleroy@kernel.org, linuxppc-dev@lists.ozlabs.org, pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, linux-riscv@lists.infradead.org, agordeev@linux.ibm.com, gerald.schaefer@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, linux-s390@vger.kernel.org, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, Hongru Zhang Subject: Re: [PATCH v6] mm: retry page faults once under the per-VMA lock Message-ID: References: <20260911025613.1220845-1-zhanghongru@xiaomi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 4960640004 X-Stat-Signature: sfc5td18j7sx4xrumi84bmdzozhnu5tx X-Rspam-User: X-HE-Tag: 1790549709-634525 X-HE-Meta: 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 SEqE1pDR +uffw29yZiBUAco6KIa4YP9Zz1ZNYbRYknEiQjig0GJYzXMjfD83sGCvANcXgICETwf5xMBqyaMD3m3iEDPedzhUH+cBs7UX1eVEAkdg1BW283JeDpX2vg2Oahv3GAhIv5lsDsQ3w+VgUEGTZJDrO/u8IhU23zZQZmT/49gkvK2By6JRl3wkWBnzn3aqcJ/84qUXZSoR3dTL30YzHA3/Wn4uwD71QxauqZMHQH90VXT1B88PAgyBEK83/Xw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 22, 2026 at 09:55:23AM +0100, Lorenzo Stoakes (ARM) wrote: > On Mon, Sep 21, 2026 at 07:57:23PM +0100, Matthew Wilcox wrote: > > more to say on this in two weeks at Plumbers. > > I look forward to it :) So while doing my slides, I realised that what we need to avoid doing is (a) sleeping while holding the mmap_lock (b) returning RETRY while holding the VMA lock And that turns out to be as simple as this patch: diff --git a/include/linux/mm.h b/include/linux/mm.h index dd09c438fa23..94ed2333f8d8 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -723,6 +723,8 @@ enum { */ static inline bool fault_flag_allow_retry_first(enum fault_flag flags) { + if (flags & FAULT_FLAG_VMA_LOCK) + return false; return (flags & FAULT_FLAG_ALLOW_RETRY) && (!(flags & FAULT_FLAG_TRIED)); } OK, this is a hack. The function is spectacularly badly named, and needs to be renamed before a patch can go upstream. But this should fix the contention on mmap_lock. Could somebody try it? I've verified it boots and runs some userspace fine, but I don't have the workload to test the contention.