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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0033EC61DA4 for ; Thu, 16 Feb 2023 15:45:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230201AbjBPPpy (ORCPT ); Thu, 16 Feb 2023 10:45:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48360 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229642AbjBPPpw (ORCPT ); Thu, 16 Feb 2023 10:45:52 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 546621BD8 for ; Thu, 16 Feb 2023 07:45:51 -0800 (PST) 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=vKirnekWaY/7YPqBImOqS8So3dx7/6DOy0i+rRDyZWU=; b=v4Efi6nPZA8YmfeKqb5WLenlFD 0k/p7dZ0EdA4YcHjqljvXqOOGSthJzq++39zRp6/q2Fu4rML04k+dAt34kXAqraSx5+SMXuzcqQsy UqRfvsgKz+ns+xawbSRrvEqH2FL8wQw/a2euo4DuP0kKao3/m6HUeqG2HOLFnEz+essxCs3IK9fMo uXzSIf1j9gWIzAaDkTPeMbpnqt2dAqsOp5NQ2VRixq/5jMSgTzhQAV/Ozc5SeckJizTH65WZjobHc GsL2aTYFqint8RVP1arhPmGAA0U8cD3Uk++dP8hyMS3q3LIFjgWduyiTqRr6+sS5D3YudYdBxBLRG 3NhSq/pQ==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pSgRD-008WXZ-IG; Thu, 16 Feb 2023 15:44:47 +0000 Date: Thu, 16 Feb 2023 15:44:47 +0000 From: Matthew Wilcox To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com, will@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, chriscli@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, rppt@kernel.org, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, leewalsh@google.com, posk@google.com, michalechner92@googlemail.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v3 26/35] mm: fall back to mmap_lock if vma->anon_vma is not yet set Message-ID: References: <20230216051750.3125598-1-surenb@google.com> <20230216051750.3125598-27-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230216051750.3125598-27-surenb@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 15, 2023 at 09:17:41PM -0800, Suren Baghdasaryan wrote: > When vma->anon_vma is not set, page fault handler will set it by either > reusing anon_vma of an adjacent VMA if VMAs are compatible or by > allocating a new one. find_mergeable_anon_vma() walks VMA tree to find > a compatible adjacent VMA and that requires not only the faulting VMA > to be stable but also the tree structure and other VMAs inside that tree. > Therefore locking just the faulting VMA is not enough for this search. > Fall back to taking mmap_lock when vma->anon_vma is not set. This > situation happens only on the first page fault and should not affect > overall performance. I think I asked this before, but don't remember getting an aswer. Why do we defer setting anon_vma to the first fault? Why don't we set it up at mmap time?