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 DCB6BCFB43F for ; Mon, 7 Oct 2024 07:06:51 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6DD896B0104; Mon, 7 Oct 2024 03:06:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 68DA06B0105; Mon, 7 Oct 2024 03:06:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 57BD66B0106; Mon, 7 Oct 2024 03:06:51 -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 39F976B0104 for ; Mon, 7 Oct 2024 03:06:51 -0400 (EDT) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id DEF3E1612DB for ; Mon, 7 Oct 2024 07:06:50 +0000 (UTC) X-FDA: 82645923780.18.5A0A27D Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) by imf13.hostedemail.com (Postfix) with ESMTP id 4699920008 for ; Mon, 7 Oct 2024 07:06:46 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b=kbZl2yLI; dmarc=none; spf=none (imf13.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.92.199) smtp.mailfrom=peterz@infradead.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1728284767; a=rsa-sha256; cv=none; b=BinRziv/Dqkc9jKfFI/YFfDbIAt0qfRsWnAk4ntRxnanTnzzLOkAJPdieCFGCHWjq3tv/8 f7iRlOOUAMdzLvam7MEdTySfEjHIw0qT43WzHqa6XRgqzziVYbFfnyNnZoy7Eh4249Gp4o e/zmsoEq1aXKCeV0zOVs/o0XLCLseJE= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b=kbZl2yLI; dmarc=none; spf=none (imf13.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.92.199) smtp.mailfrom=peterz@infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1728284767; 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=WPrGACetzn240lxkdUEDnFIeJe4VvQIHLBhegiGUuD8=; b=XZs7VSD37DhTCDyQ3TfcypPPefx3kEeb0yUMifXRbGv4EKaGOqmXJyxK+rbjSMSz0NamrF UxmFAfs2XHod2/Aw/m2fNeM6YXLh+TcDHUIfL/yJsWI6OtHYMoXDiMjwG8Q4iVmcqIHrYJ 76k1x+0tqZFPgKQ8Lfe5oW6ZFrQSnLU= 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:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=WPrGACetzn240lxkdUEDnFIeJe4VvQIHLBhegiGUuD8=; b=kbZl2yLI7r24lQNgu54c9qhvF8 lV9ZOhzm0IWhCk97HGiqo6tTyV7M1r7fvKtrXu1ZbtJ5Yz2qzfmYi3XCKDVyY0Y2kzfWwxoi2JjyS f0fedCVjGXq7A0YlId+p5Mn3tgowZ20sS3RxQl1AYPLGzm+VyjLKwqo97s+3U/CnEn5uuX2zgPfMm K/LYc5j5hbgn0nl7Bb8/PvxXhOr61coobajXrXOaV8nd+iE5qtFgUJnsOOnPHJ74sj0bl2Z6ZXIQG A+YMYwyA3kPWNWuL/YAQuxnUeiyhR2N0BIsGE3zyUURj6GVK8ChjWPOyfXLKD6R0YEx4v5u0qs1rN aTNb3RDg==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1sxhp6-00000004NYw-1PAI; Mon, 07 Oct 2024 07:06:28 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 5FF6A30088D; Mon, 7 Oct 2024 09:06:27 +0200 (CEST) Date: Mon, 7 Oct 2024 09:06:27 +0200 From: Peter Zijlstra To: Linus Torvalds Cc: Mathieu Desnoyers , Andrew Morton , linux-kernel@vger.kernel.org, Nicholas Piggin , Michael Ellerman , Greg Kroah-Hartman , Sebastian Andrzej Siewior , "Paul E. McKenney" , Will Deacon , Boqun Feng , Alan Stern , John Stultz , Neeraj Upadhyay , Frederic Weisbecker , Joel Fernandes , Josh Triplett , Uladzislau Rezki , Steven Rostedt , Lai Jiangshan , Zqiang , Ingo Molnar , Waiman Long , Mark Rutland , Thomas Gleixner , Vlastimil Babka , maged.michael@gmail.com, Mateusz Guzik , Jonas Oberhauser , rcu@vger.kernel.org, linux-mm@kvack.org, lkmm@lists.linux.dev Subject: Re: [RFC PATCH 0/4] sched+mm: Track lazy active mm existence with hazard pointers Message-ID: <20241007070627.GC18071@noisy.programming.kicks-ass.net> References: <20241002010205.1341915-1-mathieu.desnoyers@efficios.com> <20241005161537.GB18071@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 4699920008 X-Rspamd-Server: rspam01 X-Stat-Signature: qggftaxcfk8t3x8895m7w4wx5q59jf6a X-HE-Tag: 1728284806-685493 X-HE-Meta: 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 0MDNLPTs maowqW+iyx/af3ekuYWxjMaZHCid/S1DJp3lNW88/RlLoMowquu98spHNX4LztsXcejbp/s8UF66GiXyZQyDSggftjR8H3SGZw9nQq5ch3LSKt8zfmV4TOvkIQNTSGn60d1nJp418sDxia8Zz4C+R+a1hK02d4uu2TvwSjJ7Bi7SL6awfZBSK32rgnEci091gBKdgWRua6Zl0k8pE5/tPTBUZTBjgPkYWNGriH4VKSvOf7c5fhlwirBc5J8WI5+ex+ai7CVcNyVTeFgVtMOg2fNKYfM/i7N1+DX+pb2xRW3hQ2m+MWo9DH7clhwSt1Cgvsd+LNUhhtpC3Hru9BmsYlC3xSz+VkQVTuNM6 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 Sat, Oct 05, 2024 at 09:56:24AM -0700, Linus Torvalds wrote: > On Sat, 5 Oct 2024 at 09:16, Peter Zijlstra wrote: > > > > On Wed, Oct 02, 2024 at 10:39:15AM -0700, Linus Torvalds wrote: > > > So I think the real issue is that "active_mm" is an old hack from a > > > bygone era when we didn't have the (much more involved) full TLB > > > tracking. > > > > I still seem to have these patches that neither Andy nor I ever managed > > to find time to finish: > > > > https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=x86/lazy > > Yes, that looks very much like what I had in mind. > > In fact, it looks a lot smaller and simpler than what my mental model was. > > I was thinking I'd do it by removing "active_mm" entirely from 'struct > task_struct', and turn it into a per-cpu variable instead, and then > try to massage that into some global new world order. That patch > series you point to seems to be much simpler and clearer. > > Of course, you also say "never managed to finish", so presumably > there's something completely broken in that series, and it doesn't > actually work? Last time I tried it, it worked fine. I just didn't get around to actually fully thinking it trough and making sure nothing subtle was broken etc. Pesky details and such..