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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C703CC4741F for ; Wed, 23 Sep 2020 21:12:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1CDFB214F1 for ; Wed, 23 Sep 2020 21:12:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1CDFB214F1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 19C326B0003; Wed, 23 Sep 2020 17:12:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 125C16B0037; Wed, 23 Sep 2020 17:12:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 014AF6B005A; Wed, 23 Sep 2020 17:12:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0044.hostedemail.com [216.40.44.44]) by kanga.kvack.org (Postfix) with ESMTP id DD6AA6B0003 for ; Wed, 23 Sep 2020 17:12:42 -0400 (EDT) Received: from smtpin26.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 9ACA53636 for ; Wed, 23 Sep 2020 21:12:42 +0000 (UTC) X-FDA: 77295575364.26.cart55_5808de827159 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin26.hostedemail.com (Postfix) with ESMTP id 732F51804B670 for ; Wed, 23 Sep 2020 21:12:42 +0000 (UTC) X-HE-Tag: cart55_5808de827159 X-Filterd-Recvd-Size: 5027 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Wed, 23 Sep 2020 21:12:41 +0000 (UTC) Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0CA3D2145D; Wed, 23 Sep 2020 21:12:35 +0000 (UTC) Date: Wed, 23 Sep 2020 17:12:34 -0400 From: Steven Rostedt To: Thomas Gleixner Cc: peterz@infradead.org, Linus Torvalds , LKML , linux-arch , Paul McKenney , the arch/x86 maintainers , Sebastian Andrzej Siewior , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Will Deacon , Andrew Morton , Linux-MM , Russell King , Linux ARM , Chris Zankel , Max Filippov , linux-xtensa@linux-xtensa.org, Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , David Airlie , Daniel Vetter , intel-gfx , dri-devel , Ard Biesheuvel , Herbert Xu , Vineet Gupta , "open list\:SYNOPSYS ARC ARCHITECTURE" , Arnd Bergmann , Guo Ren , linux-csky@vger.kernel.org, Michal Simek , Thomas Bogendoerfer , linux-mips@vger.kernel.org, Nick Hu , Greentime Hu , Vincent Chen , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev , "David S. Miller" , linux-sparc Subject: Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends Message-ID: <20200923171234.0001402d@oasis.local.home> In-Reply-To: <874kno9pr9.fsf@nanos.tec.linutronix.de> References: <20200919091751.011116649@linutronix.de> <87mu1lc5mp.fsf@nanos.tec.linutronix.de> <87k0wode9a.fsf@nanos.tec.linutronix.de> <87eemwcpnq.fsf@nanos.tec.linutronix.de> <87a6xjd1dw.fsf@nanos.tec.linutronix.de> <87sgbbaq0y.fsf@nanos.tec.linutronix.de> <20200923084032.GU1362448@hirez.programming.kicks-ass.net> <20200923115251.7cc63a7e@oasis.local.home> <874kno9pr9.fsf@nanos.tec.linutronix.de> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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: On Wed, 23 Sep 2020 22:55:54 +0200 Thomas Gleixner wrote: > > Perhaps make migrate_disable() an anonymous local_lock()? > > > > This should lower the SHC in theory, if you can't have stacked migrate > > disables on the same CPU. > > I'm pretty sure this ends up in locking hell pretty fast and aside of > that it's not working for scenarios like: > > kmap_local(); > migrate_disable(); > ... > > copy_from_user() > -> #PF > -> schedule() > > which brought us into that discussion in the first place. You would stop > any other migrate disable user from running until the page fault is > resolved... Then scratch the idea of having anonymous local_lock() and just bring local_lock in directly? Then have a kmap local lock, which would only block those that need to do a kmap. Now as for migration disabled nesting, at least now we would have groupings of this, and perhaps the theorists can handle that. I mean, how is this much different that having a bunch of tasks blocked on a mutex with the owner is pinned on a CPU? migrate_disable() is a BKL of pinning affinity. If we only have local_lock() available (even on !RT), then it makes the blocking in groups. At least this way you could grep for all the different local_locks in the system and plug that into the algorithm for WCS, just like one would with a bunch of mutexes. -- Steve