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_1 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 D5AA9C43464 for ; Fri, 18 Sep 2020 09:36:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 73D9621D7B for ; Fri, 18 Sep 2020 09:36:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726416AbgIRJge (ORCPT ); Fri, 18 Sep 2020 05:36:34 -0400 Received: from mx2.suse.de ([195.135.220.15]:41702 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726109AbgIRJgd (ORCPT ); Fri, 18 Sep 2020 05:36:33 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 0D565B114; Fri, 18 Sep 2020 09:37:06 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id D0CB81E12E1; Fri, 18 Sep 2020 11:36:30 +0200 (CEST) Date: Fri, 18 Sep 2020 11:36:30 +0200 From: Jan Kara To: Ira Weiny Cc: Jason Gunthorpe , Peter Xu , Linus Torvalds , John Hubbard , Leon Romanovsky , Linux-MM , Linux Kernel Mailing List , "Maya B . Gokhale" , Yang Shi , Marty Mcfadden , Kirill Shutemov , Oleg Nesterov , Jann Horn , Jan Kara , Kirill Tkhai , Andrea Arcangeli , Christoph Hellwig , Andrew Morton Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification Message-ID: <20200918093630.GC18920@quack2.suse.cz> References: <20200917112538.GD8409@ziepe.ca> <20200917181411.GA133226@xz-x1> <20200917190332.GB133226@xz-x1> <20200917200638.GM8409@ziepe.ca> <20200917214059.GA162800@xz-x1> <20200917220900.GO8409@ziepe.ca> <20200917224857.GF2540965@iweiny-DESK2.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200917224857.GF2540965@iweiny-DESK2.sc.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 17-09-20 15:48:57, Ira Weiny wrote: > On Thu, Sep 17, 2020 at 07:09:00PM -0300, Jason Gunthorpe wrote: > > On Thu, Sep 17, 2020 at 05:40:59PM -0400, Peter Xu wrote: > > > On Thu, Sep 17, 2020 at 01:35:56PM -0700, Linus Torvalds wrote: > > > > For that to happen, we'd need to have the vma flag so that we wouldn't > > > > have any worry about non-pinners, but as you suggested, I think even > > > > just a mm-wide counter - or flag - to deal with the fast-bup case is > > > > likely perfectly sufficient. > > > > > > Would mm_struct.pinned_vm suffice? > > > > I think that could be a good long term goal > > > > IIRC last time we dug into the locked_vm vs pinned_vm mess it didn't > > get fixed. There is a mix of both kinds, as you saw, and some > > resistance I don't clearly remember to changing it. > > > > My advice for this -rc fix is to go with a single bit in the mm_struct > > set on any call to pin_user_pages* > > > > Then only users using pin_user_pages and forking are the only ones who > > would ever do extra COW on fork. I think that is OK for -rc, this > > workload should be rare due to the various historical issues. Anyhow, > > a slow down regression is better than a it is broken regression. > > > > This can be improved into a counter later. Due to the pinned_vm > > accounting all call sites should have the mm_struct at unpin, but I > > have a feeling it will take a alot of driver patches to sort it all > > out. > > Agreed. The HFI1 driver for example increments/decrements pinned_vm on it's > own. I've kind of always felt dirty for that... > > I think long term it would be better to move this accounting to > pin_user_pages() but Jason is correct that I think that is going to be too > complex for an rc. Moving accounting to pin_user_pages() won't be simple because you need to unaccount on unpin. And that can happen from a different task context (e.g. IRQ handler for direct IO) so we won't have proper mm_struct available. > Could we move pinned_vm out of the drivers/rdma subsystem? I'd love to because IMO it's a mess... Honza -- Jan Kara SUSE Labs, CR