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]) by smtp.lore.kernel.org (Postfix) with ESMTP id CD048E77184 for ; Thu, 19 Dec 2024 18:46:58 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5A79B6B007B; Thu, 19 Dec 2024 13:46:58 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 530BB6B0082; Thu, 19 Dec 2024 13:46:58 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3AB6B6B0083; Thu, 19 Dec 2024 13:46:58 -0500 (EST) 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 1E1F46B007B for ; Thu, 19 Dec 2024 13:46:58 -0500 (EST) Received: from smtpin06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 87038801AA for ; Thu, 19 Dec 2024 18:46:57 +0000 (UTC) X-FDA: 82912589172.06.8A9F341 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) by imf11.hostedemail.com (Postfix) with ESMTP id ADA6C40023 for ; Thu, 19 Dec 2024 18:46:24 +0000 (UTC) Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b="S/wi1bNe"; spf=none (imf11.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.92.199) smtp.mailfrom=peterz@infradead.org; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1734634000; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=rGpeIQU8OFNXXoe0FS/CeUx+kNOrcVNpVk7LZwVhvWA=; b=C0MLcj9Nwl0kqVQtzHM65AGJC1W6YWsfDjDEnLIs9v1NvAMfGlQBKIj8KV5cLdwJYLwoPJ xBG7FaUwnFpwv2QFOhwxsDThowTaM5hyDQPYIIrmVzUEAbOyPdjhrzntryruhCSDhKD/wk kIUWsiFhhmjnae668kAIv8fsWM9jRSU= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b="S/wi1bNe"; spf=none (imf11.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.92.199) smtp.mailfrom=peterz@infradead.org; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1734634000; a=rsa-sha256; cv=none; b=Nu4LYi4pq28g0Qj6BZW0iHJa4AyrqnRyIH93p9w2HpjCjvStSVRXzCFmS4qHuiKAKMwh6j sPxAG/WL5t3IqQh3iiJwaejdnbXtZP/O1dpwspGwOoXDLAqZGZoBS9QT5bd6S3PEm58zP+ mX4KOo0xYFfH9N8m/KVRDZGowJfQwjE= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:To:From:Date:Sender:Reply-To:Cc: Content-Transfer-Encoding:Content-ID:Content-Description; bh=rGpeIQU8OFNXXoe0FS/CeUx+kNOrcVNpVk7LZwVhvWA=; b=S/wi1bNeQ9Q4i3rS/866YGgl2l sxjX4PZy8ejVi0QwRX6tnAaN4aIElD4TQue2Y0UGZI0RS7yqlyyCxvy/wm/4+D+OTsNH0gEMajZ1x AgCzSk6L82f/7uXvbHOXFTfWFaMyr5IkLFdYjbX+3g6wafzr4saIOUb9hQcqvaNNsLkhfY/X9LxVq u33g34oQAoGd/pda55FN+xUn6SdvlNPTb57LJb0TcvPwAI3t8ai+kuZ4IcRgbzMmHrMZ1o/YXXkmj xk0Lc8tD2brqYHKLRljGjNIfjDvRkDqkKG65eRrTr434YjeKdsAQl/vD8ZeX3B4RwK9Cj0C4LLfYH 4E2LY/5A==; Received: from 77-249-17-89.cable.dynamic.v4.ziggo.nl ([77.249.17.89] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tOLXn-00000005Ucw-3lLs; Thu, 19 Dec 2024 18:46:44 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 4CEA330031E; Thu, 19 Dec 2024 19:46:42 +0100 (CET) Date: Thu, 19 Dec 2024 19:46:42 +0100 From: Peter Zijlstra To: "Liam R. Howlett" , Suren Baghdasaryan , akpm@linux-foundation.org, willy@infradead.org, lorenzo.stoakes@oracle.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, lokeshgidra@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, klarasmodin@gmail.com, corbet@lwn.net, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v6 10/16] mm: replace vm_lock and detached flag with a reference count Message-ID: <20241219184642.GF26279@noisy.programming.kicks-ass.net> References: <20241219091334.GC26551@noisy.programming.kicks-ass.net> <20241219112011.GA34942@noisy.programming.kicks-ass.net> <20241219174235.GD26279@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: ADA6C40023 X-Stat-Signature: ckfz118t3rxg4o8h5dijzcnmua3xfzre X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1734633984-669584 X-HE-Meta: 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 7WkkLmdM WMCpFmn/18nkgqcIlNHNFafz4x/hPMLTIZlHb8DuHIF6H+3MrZC5KSLPqXWETkvWDSRLdgd1QyjreTpntkjNqfGR//v9sKj8Qv7BMf+utuSXhaBi4E9S94G186nrtgfu/I7wDujatVyiWXkMCTvOo8/0QbD77dxgpO0DTUjjnHSNs15K5ewTWTD3z57ISos5lztYGUOsvJBs3wqYrQpJFYscwBtNtCewzyggld9S5oZevXPgoH/6UGUP/bw== 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 Thu, Dec 19, 2024 at 01:18:23PM -0500, Liam R. Howlett wrote: > > For RCU lookups only the mas tree matters -- and its left present there. > > > > If you really want to block RCU readers, I would suggest punching a hole > > in the mm_mt. All the traditional code won't notice anyway, this is all > > with mmap_lock held for writing. > > We don't want to block all rcu readers, we want to block the rcu readers > that would see the problem - that is, anyone trying to read a particular > area. > > Right now we can page fault in unpopulated vmas while writing other vmas > to the tree. We are also moving more users to rcu reading to use the > vmas they need without waiting on writes to finish. > > Maybe I don't understand your suggestion, but I would think punching a > hole would lose this advantage? My suggestion was to remove the range stuck in mas_detach from mm_mt. That is exactly the affected range, no?