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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 2D094C004D3 for ; Mon, 22 Oct 2018 13:27:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BBAE620853 for ; Mon, 22 Oct 2018 13:27:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BBAE620853 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728703AbeJVVqb (ORCPT ); Mon, 22 Oct 2018 17:46:31 -0400 Received: from mx2.suse.de ([195.135.220.15]:46678 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728030AbeJVVqb (ORCPT ); Mon, 22 Oct 2018 17:46:31 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 19518AFF6; Mon, 22 Oct 2018 13:27:55 +0000 (UTC) Subject: Re: [PATCH 2/2] mm, thp: consolidate THP gfp handling into alloc_hugepage_direct_gfpmask To: Michal Hocko , Andrew Morton Cc: "Kirill A. Shutemov" , Mel Gorman , David Rientjes , Andrea Argangeli , Zi Yan , Stefan Priebe - Profihost AG , linux-mm@kvack.org, LKML References: <20180925120326.24392-1-mhocko@kernel.org> <20180925120326.24392-3-mhocko@kernel.org> <20180926133039.y7o5x4nafovxzh2s@kshutemo-mobl1> <20180926141708.GX6278@dhcp22.suse.cz> <20180926142227.GZ6278@dhcp22.suse.cz> <20181018191147.33e8d5e1ebd785c06aab7b30@linux-foundation.org> <20181019080657.GJ18839@dhcp22.suse.cz> From: Vlastimil Babka Openpgp: preference=signencrypt Autocrypt: addr=vbabka@suse.cz; prefer-encrypt=mutual; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSFWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmNvbT7CwZcEEwEKAEECGwMFCwkIBwMFFQoJCAsFFgIDAQAC HgECF4ACGQEWIQSpQNQ0mSwujpkQPVAiT6fnzIKmZAUCWi/zTwUJBbOLuQAKCRAiT6fnzIKm ZIpED/4jRN/6LKZZIT4R2xoou0nJkBGVA3nfb+mUMgi3uwn/zC+o6jjc3ShmP0LQ0cdeuSt/ t2ytstnuARTFVqZT4/IYzZgBsLM8ODFY5vGfPw00tsZMIfFuVPQX3xs0XgLEHw7/1ZCVyJVr mTzYmV3JruwhMdUvIzwoZ/LXjPiEx1MRdUQYHAWwUfsl8lUZeu2QShL3KubR1eH6lUWN2M7t VcokLsnGg4LTajZzZfq2NqCKEQMY3JkAmOu/ooPTrfHCJYMF/5dpi8YF1CkQF/PVbnYbPUuh dRM0m3NzPtn5DdyfFltJ7fobGR039+zoCo6dFF9fPltwcyLlt1gaItfX5yNbOjX3aJSHY2Vc A5T+XAVC2sCwj0lHvgGDz/dTsMM9Ob/6rRJANlJPRWGYk3WVWnbgW8UejCWtn1FkiY/L/4qJ UsqkId8NkkVdVAenCcHQmOGjRQYTpe6Cf4aQ4HGNDeWEm3H8Uq9vmHhXXcPLkxBLRbGDSHyq vUBVaK+dAwAsXn/5PlGxw1cWtur1ep7RDgG3vVQDhIOpAXAg6HULjcbWpBEFaoH720oyGmO5 kV+yHciYO3nPzz/CZJzP5Ki7Q1zqBb/U6gib2at5Ycvews+vTueYO+rOb9sfD8BFTK386LUK uce7E38owtgo/V2GV4LMWqVOy1xtCB6OAUfnGDU2EM7ATQRbGTU1AQgAn0H6UrFiWcovkh6E XVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQLa1PQDUi6j00ChlcR66g9/V0sPIcSutacPKf dKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMhFmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCT sTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sfbAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZO rIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq+aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahK tQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4njQARAQABwsF8BBgBCgAmFiEEqUDUNJksLo6Z ED1QIk+n58yCpmQFAlsZNTUCGwwFCQPCZwAACgkQIk+n58yCpmQ83g/9Frg1sRMdGPn98zV+ O2eC3h0p5f/oxxQ8MhG5znwHoW4JDG2TuxfcQuz7X7Dd5JWscjlw4VFJ2DD+IrDAGLHwPhCr RyfKalnrbYokvbClM9EuU1oUuh7k+Sg5ECNXEsamW9AiWGCaKWNDdHre3Lf4xl+RJWxghOVW RiUdpLA/a3yDvJNVr6rxkDHQ1P24ZZz/VKDyP+6g8aty2aWEU0YFNjI+rqYZb2OppDx6fdma YnLDcIfDFnkVlDmpznnGCyEqLLyMS3GH52AH13zMT9L9QYgT303+r6QQpKBIxAwn8Jg8dAlV OLhgeHXKr+pOQdFf6iu2sXlUR4MkO/5KWM1K0jFR2ug8Pb3aKOhowVMBT64G0TXhQ/kX4tZ2 ZF0QZLUCHU3Cigvbu4AWWVMNDEOGD/4sn9OoHxm6J04jLUHFUpFKDcjab4NRNWoHLsuLGjve Gdbr2RKO2oJ5qZj81K7os0/5vTAA4qHDP2EETAQcunTn6aPlkUnJ8aw6I1Rwyg7/XsU7gQHF IM/cUMuWWm7OUUPtJeR8loxZiZciU7SMvN1/B9ycPMFs/A6EEzyG+2zKryWry8k7G/pcPrFx O2PkDPy3YmN1RfpIX2HEmnCEFTTCsKgYORangFu/qOcXvM83N+2viXxG4mjLAMiIml1o2lKV cqmP8roqufIAj+Ohhzs= Message-ID: <583b20e5-4925-e175-1533-5c2d2bab9192@suse.cz> Date: Mon, 22 Oct 2018 15:27:54 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <20181019080657.GJ18839@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/19/18 10:06 AM, Michal Hocko wrote: > On Thu 18-10-18 19:11:47, Andrew Morton wrote: >> On Wed, 26 Sep 2018 16:22:27 +0200 Michal Hocko wrote: >> >>>> MPOL_PREFERRED is handled by policy_node() before we call __alloc_pages_nodemask. >>>> __GFP_THISNODE is applied only when we are not using >>>> __GFP_DIRECT_RECLAIM which is handled in alloc_hugepage_direct_gfpmask >>>> now. >>>> Lastly MPOL_BIND wasn't handled explicitly but in the end the removed >>>> late check would remove __GFP_THISNODE for it as well. So in the end we >>>> are doing the same thing unless I miss something >>> >>> Forgot to add. One notable exception would be that the previous code >>> would allow to hit >>> WARN_ON_ONCE(policy->mode == MPOL_BIND && (gfp & __GFP_THISNODE)); >>> in policy_node if the requested node (e.g. cpu local one) was outside of >>> the mbind nodemask. This is not possible now. We haven't heard about any >>> such warning yet so it is unlikely that it happens though. >> >> Perhaps a changelog addition is needed to cover the above? > > : THP allocation mode is quite complex and it depends on the defrag > : mode. This complexity is hidden in alloc_hugepage_direct_gfpmask from a > : large part currently. The NUMA special casing (namely __GFP_THISNODE) is > : however independent and placed in alloc_pages_vma currently. This both > : adds an unnecessary branch to all vma based page allocation requests and > : it makes the code more complex unnecessarily as well. Not to mention > : that e.g. shmem THP used to do the node reclaiming unconditionally > : regardless of the defrag mode until recently. This was not only > : unexpected behavior but it was also hardly a good default behavior and I > : strongly suspect it was just a side effect of the code sharing more than > : a deliberate decision which suggests that such a layering is wrong. > : > : Moreover the oriinal code allowed to trigger > : WARN_ON_ONCE(policy->mode == MPOL_BIND && (gfp & __GFP_THISNODE)); > : in policy_node if the requested node (e.g. cpu local one) was outside of > : the mbind nodemask. This is not possible now. We haven't heard about any > : such warning yet so it is unlikely that it happens but still a signal of > : a wrong code layering. Ah, as I said in the other mail, I think it's inaccurate, the warning was not possible to hit. There's also a slight difference wrt MPOL_BIND. The previous code would avoid using __GFP_THISNODE if the local node was outside of policy_nodemask(). After your patch __GFP_THISNODE is avoided for all MPOL_BIND policies. So there's a difference that if local node is actually allowed by the bind policy's nodemask, previously __GFP_THISNODE would be added, but now it won't be. I don't think it matters that much though, but maybe the changelog could say that (instead of the inaccurate note about warning). Note the other policy where nodemask is relevant is MPOL_INTERLEAVE, and that's unchanged by this patch. When that's addressed, you can add Acked-by: Vlastimil Babka (Note I also agree with patch 1/2 but didn't think it was useful to formally ack it on top of Mel's ack supported by actual measurements, as we're all from the same company). > : Get rid of the thp special casing from alloc_pages_vma and move the logic > : to alloc_hugepage_direct_gfpmask. __GFP_THISNODE is applied to > : the resulting gfp mask only when the direct reclaim is not requested and > : when there is no explicit numa binding to preserve the current logic. > : > : This allows for removing alloc_hugepage_vma as well. > > Better? > >> I assume that David's mbind() concern has gone away. > > Either I've misunderstood it or it was not really a real issue. >