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=-7.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=unavailable 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 2E6F5C10F14 for ; Thu, 18 Apr 2019 14:27:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C885A217D7 for ; Thu, 18 Apr 2019 14:27:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C885A217D7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 501546B0005; Thu, 18 Apr 2019 10:27:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 48A1F6B0006; Thu, 18 Apr 2019 10:27:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3520A6B0007; Thu, 18 Apr 2019 10:27:43 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) by kanga.kvack.org (Postfix) with ESMTP id 130596B0005 for ; Thu, 18 Apr 2019 10:27:43 -0400 (EDT) Received: by mail-qk1-f199.google.com with SMTP id b188so1843999qkg.15 for ; Thu, 18 Apr 2019 07:27:43 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-original-authentication-results:x-gm-message-state:date:from:to :cc:subject:message-id:references:mime-version:content-disposition :content-transfer-encoding:in-reply-to:user-agent; bh=M9YeBkyZkesFqHmcfbg7FiAHZxxm2bJznV6I0E4+r4k=; b=uHaulP8mMaaBmRkwaRlZonHgnh32TOlpEKZazkh9DTM8fuxc10mfDqlfgYhJu0yzmC gGAiYMz/IxEALDS1g5DNVj4bJ3xXGKn98gbbj0EnGkhHVRmGLF68i/zNgCNtQq7ed0S0 bnPNaPQ3/H+miRrKhW2A9P1pkVe7sTaN1RdtvA/XwoDMOiutI2Lz9ttwsTt4mlMO2+L0 CVU0VRnWfqxEN1xYXJeLlEQe9mYZd9NvCwGBYeSTBVLjBBC17aCKXwfofGpaPDVHlJV2 WJ7E5WBHBTaAPdspUnBxMgupY9sb8XHcnF01RKT39gkSQkLsiKp5WfMVJq/4wHvlsoqK sFHg== X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jglisse@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com X-Gm-Message-State: APjAAAU+pC9WO4tuvalz8YulF1oldfCfBCUdqfh2sROftRttfyvD+aas o1GpzcvfRJA2QMJNlyoYs50gR5iZkV2wC/sjagPtdMlM+N/Dk5p5yBhwcfh/fr65+1AMyDpzA1h ytRns3aEGN7Ul3CPxSBHHv56jcKaq0X9yEdAiFg8/lGmpfXRNHkbQWIXw2Gsevz9Vyg== X-Received: by 2002:a0c:b758:: with SMTP id q24mr30689917qve.31.1555597662811; Thu, 18 Apr 2019 07:27:42 -0700 (PDT) X-Google-Smtp-Source: APXvYqwLUIAhqO3ux5KnTs+RLFZWDV+5r3PohlilPigFaSohQy0BcSaNjbpRUoBZAd+2H4zMkhme X-Received: by 2002:a0c:b758:: with SMTP id q24mr30689854qve.31.1555597661946; Thu, 18 Apr 2019 07:27:41 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1555597661; cv=none; d=google.com; s=arc-20160816; b=ZOmExwqWajyGM5aQWzPJBFZMIC9cGWTto2oXMEk3Aw601qJmMhQ8TwnOi2SALptKqp y+I+1zNVUVBoaMb8UtDr2QsvhiGEZlpYqC9Gf/soGagbUAufjfje5s+1e29i31Esvo21 Kk1jlF+z0QomuOFKYkGEX8f4vWPMjO5hSN2XO3yuIDIHPGFqbpg+ssd5mip2+JxV/aK7 bqCFFprwcYX2sQcHfnyea3ZzlgkLw2OtVdYTqiU8fIbGiIGSFlqE56w3C0SAHdUpyA/e hZS9LjZt6PRXK3TV+RQ+FgFOyUVfTUxjbmgMfpw9C6nfVcmjgAkwqG1bRGFcMA0uLpj5 tGxQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-transfer-encoding :content-disposition:mime-version:references:message-id:subject:cc :to:from:date; bh=M9YeBkyZkesFqHmcfbg7FiAHZxxm2bJznV6I0E4+r4k=; b=XcjGNPdT5NCRZboCmFY9xw1pQg7mbVSw8/wyIpe8IdlPp0x2bxGRjI75gvlquryToU 8771AD97LKnMEEe2Vhb/lauzv6BqWHO1rxA2OnmNrtf0J+D0rmA4OJB4oLpXXQpgdu5g Bj9GZy3+qHuRTSoG4DqJG6U/4GyO4LyR95hnzjzuqDj9S2fHaDoL9Wc/E/S+dai5Yor8 lgkIfBcw6qDN6IXtwD5WGVeFFhVKEnMXX1DQ2h5N4HJxoP15sGWuREm9yHJIxtBWLQej TRFu6o7m2oxJIB0O10XGYNJjMWs/5UsIerNHSHcU6k9kW4DcNiW0I7EBaqHRnumkjlx0 1Kkw== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jglisse@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id 7si1660710qvg.130.2019.04.18.07.27.41 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 18 Apr 2019 07:27:41 -0700 (PDT) Received-SPF: pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jglisse@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jglisse@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D1F1DDBD73; Thu, 18 Apr 2019 14:27:40 +0000 (UTC) Received: from redhat.com (unknown [10.20.6.236]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 39EAC600C1; Thu, 18 Apr 2019 14:27:31 +0000 (UTC) Date: Thu, 18 Apr 2019 10:27:29 -0400 From: Jerome Glisse To: Jan Kara Cc: Dan Williams , Kent Overstreet , Boaz Harrosh , Linux Kernel Mailing List , linux-fsdevel , linux-block@vger.kernel.org, Linux MM , John Hubbard , Alexander Viro , Johannes Thumshirn , Christoph Hellwig , Jens Axboe , Ming Lei , Jason Gunthorpe , Matthew Wilcox , Steve French , linux-cifs@vger.kernel.org, samba-technical@lists.samba.org, Yan Zheng , Sage Weil , Ilya Dryomov , Alex Elder , ceph-devel@vger.kernel.org, Eric Van Hensbergen , Latchesar Ionkov , Mike Marshall , Martin Brandenburg , devel@lists.orangefs.org, Dominique Martinet , v9fs-developer@lists.sourceforge.net, Coly Li , linux-bcache@vger.kernel.org, Ernesto =?iso-8859-1?Q?A=2E_Fern=E1ndez?= Subject: Re: [PATCH v1 00/15] Keep track of GUPed pages in fs and block Message-ID: <20190418142729.GB3288@redhat.com> References: <20190411210834.4105-1-jglisse@redhat.com> <2c124cc4-b97e-ee28-2926-305bc6bc74bd@plexistor.com> <20190416185922.GA12818@kmo-pixel> <20190416194936.GD21526@redhat.com> <20190417222858.GA4146@redhat.com> <20190418104205.GA28541@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190418104205.GA28541@quack2.suse.cz> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 18 Apr 2019 14:27:41 +0000 (UTC) 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 Thu, Apr 18, 2019 at 12:42:05PM +0200, Jan Kara wrote: > On Wed 17-04-19 18:28:58, Jerome Glisse wrote: > > On Wed, Apr 17, 2019 at 02:53:28PM -0700, Dan Williams wrote: > > > On Tue, Apr 16, 2019 at 12:50 PM Jerome Glisse wrote: > > > > > > > > On Tue, Apr 16, 2019 at 12:12:27PM -0700, Dan Williams wrote: > > > > > On Tue, Apr 16, 2019 at 11:59 AM Kent Overstreet > > > > > wrote: > > > > > > > > > > > > On Tue, Apr 16, 2019 at 09:35:04PM +0300, Boaz Harrosh wrote: > > > > > > > On Thu, Apr 11, 2019 at 05:08:19PM -0400, jglisse@redhat.com wrote: > > > > > > > > From: Jérôme Glisse > > > > > > > > > > > > > > > > This patchset depends on various small fixes [1] and also on patchset > > > > > > > > which introduce put_user_page*() [2] and thus is 5.3 material as those > > > > > > > > pre-requisite will get in 5.2 at best. Nonetheless i am posting it now > > > > > > > > so that it can get review and comments on how and what should be done > > > > > > > > to test things. > > > > > > > > > > > > > > > > For various reasons [2] [3] we want to track page reference through GUP > > > > > > > > differently than "regular" page reference. Thus we need to keep track > > > > > > > > of how we got a page within the block and fs layer. To do so this patch- > > > > > > > > set change the bio_bvec struct to store a pfn and flags instead of a > > > > > > > > direct pointer to a page. This way we can flag page that are coming from > > > > > > > > GUP. > > > > > > > > > > > > > > > > This patchset is divided as follow: > > > > > > > > - First part of the patchset is just small cleanup i believe they > > > > > > > > can go in as his assuming people are ok with them. > > > > > > > > > > > > > > > > > > > > > > - Second part convert bio_vec->bv_page to bio_vec->bv_pfn this is > > > > > > > > done in multi-step, first we replace all direct dereference of > > > > > > > > the field by call to inline helper, then we introduce macro for > > > > > > > > bio_bvec that are initialized on the stack. Finaly we change the > > > > > > > > bv_page field to bv_pfn. > > > > > > > > > > > > > > Why do we need a bv_pfn. Why not just use the lowest bit of the page-ptr > > > > > > > as a flag (pointer always aligned to 64 bytes in our case). > > > > > > > > > > > > > > So yes we need an inline helper for reference of the page but is it not clearer > > > > > > > that we assume a page* and not any kind of pfn ? > > > > > > > It will not be the first place using low bits of a pointer for flags. > > > > > > > > > > > > > > That said. Why we need it at all? I mean why not have it as a bio flag. If it exist > > > > > > > at all that a user has a GUP and none-GUP pages to IO at the same request he/she > > > > > > > can just submit them as two separate BIOs (chained at the block layer). > > > > > > > > > > > > > > Many users just submit one page bios and let elevator merge them any way. > > > > > > > > > > > > Let's please not add additional flags and weirdness to struct bio - "if this > > > > > > flag is set interpret one way, if not interpret another" - or eventually bios > > > > > > will be as bad as skbuffs. I would much prefer just changing bv_page to bv_pfn. > > > > > > > > > > This all reminds of the failed attempt to teach the block layer to > > > > > operate without pages: > > > > > > > > > > https://lore.kernel.org/lkml/20150316201640.33102.33761.stgit@dwillia2-desk3.amr.corp.intel.com/ > > > > > > > > > > > > > > > > > Question though - why do we need a flag for whether a page is a GUP page or not? > > > > > > Couldn't the needed information just be determined by what range the pfn is not > > > > > > (i.e. whether or not it has a struct page associated with it)? > > > > > > > > > > That amounts to a pfn_valid() check which is a bit heavier than if we > > > > > can store a flag in the bv_pfn entry directly. > > > > > > > > > > I'd say create a new PFN_* flag, and make bv_pfn a 'pfn_t' rather than > > > > > an 'unsigned long'. > > > > > > > > > > That said, I'm still in favor of Jan's proposal to just make the > > > > > bv_page semantics uniform. Otherwise we're complicating this core > > > > > infrastructure for some yet to be implemented GPU memory management > > > > > capabilities with yet to be determined value. Circle back when that > > > > > value is clear, but in the meantime fix the GUP bug. > > > > > > > > This has nothing to do with GPU, what make you think so ? Here i am > > > > trying to solve GUP and to keep the value of knowing wether a page > > > > has been GUP or not. I argue that if we bias every page in every bio > > > > then we loose that information and thus the value. > > > > > > > > I gave the page protection mechanisms as an example that would be > > > > impacted but it is not the only one. Knowing if a page has been GUP > > > > can be useful for memory reclaimation, compaction, NUMA balancing, > > > > > > Right, this is what I was reacting to in your pushback to Jan's > > > proposal. You're claiming value for not doing the simple thing for > > > some future "may be useful in these contexts". To my knowledge those > > > things are not broken today. You're asking for the complexity to be > > > carried today for some future benefit, and I'm asking for the > > > simplicity to be maintained as much as possible today and let the > > > value of future changes stand on their own to push for more complexity > > > later. > > > > > > Effectively don't use this bug fix to push complexity for a future > > > agenda where the value has yet to be quantified. > > > > Except that this solution (biasing everyone in bio) would _more complex_ > > it is only conceptualy appealing. The changes are on the other hand much > > deeper and much riskier but you decided to ignore that and focus on some- > > thing i was just giving as an example. > > Yeah, after going and reading several places like fs/iomap.c, fs/mpage.c, > drivers/md/dm-io.c I agree with you. The places that are not doing direct > IO usually just don't hold any page reference that could be directly > attributed to the bio (and they don't drop it when bio finishes). They > rather use other means (like PageLocked, PageWriteback) to make sure the > page stays alive so mandating gup-pin reference for all pages attached to a > bio would require a lot of reworking of places that are not related to our > problem and currently work just fine. So I withdraw my suggestion. Nice in > theory, too much work in practice ;). Have you seem Boaz proposal ? I have started it and it does not look to bad (but you knwo taste and color :)) You can take a peek: https://cgit.freedesktop.org/~glisse/linux/log/?h=gup-bio-v2 I need to finish that and run fstests on bunch of different fs before posting. Dunno if i will have enough time to do that before LSF/MM. Cheers, Jérôme