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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 01EC7ECE568 for ; Mon, 24 Sep 2018 20:03:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9FDFF20C0A for ; Mon, 24 Sep 2018 20:03:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9FDFF20C0A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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 S1727241AbeIYCGx (ORCPT ); Mon, 24 Sep 2018 22:06:53 -0400 Received: from mx2.suse.de ([195.135.220.15]:58456 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725824AbeIYCGw (ORCPT ); Mon, 24 Sep 2018 22:06:52 -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 1BE3CAF71; Mon, 24 Sep 2018 20:02:59 +0000 (UTC) Date: Mon, 24 Sep 2018 22:02:58 +0200 From: Michal Hocko To: David Rientjes Cc: Andrew Morton , Vlastimil Babka , Alexey Dobriyan , "Kirill A. Shutemov" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org Subject: Re: [patch v2] mm, thp: always specify ineligible vmas as nh in smaps Message-ID: <20180924200258.GK18685@dhcp22.suse.cz> References: <20180924195603.GJ18685@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180924195603.GJ18685@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 24-09-18 21:56:03, Michal Hocko wrote: > On Mon 24-09-18 12:30:07, David Rientjes wrote: > > Commit 1860033237d4 ("mm: make PR_SET_THP_DISABLE immediately active") > > introduced a regression in that userspace cannot always determine the set > > of vmas where thp is ineligible. > > > > Userspace relies on the "nh" flag being emitted as part of /proc/pid/smaps > > to determine if a vma is eligible to be backed by hugepages. > > I was under impression that nh resp hg flags only tell about the madvise > status. How do you exactly use these flags in an application? > > Your eligible rules as defined here: > > > + [*] A process mapping is eligible to be backed by transparent hugepages (thp) > > + depending on system-wide settings and the mapping itself. See > > + Documentation/admin-guide/mm/transhuge.rst for default behavior. If a > > + mapping has a flag of "nh", it is not eligible to be backed by hugepages > > + in any condition, either because of prctl(PR_SET_THP_DISABLE) or > > + madvise(MADV_NOHUGEPAGE). PR_SET_THP_DISABLE takes precedence over any > > + MADV_HUGEPAGE. > > doesn't seem to match the reality. I do not see all the file backed > mappings to be nh marked. So is this really about eligibility rather > than the madvise status? Maybe it is just the above documentation that > needs to be updated. > > That being said, I do not object to the patch, I am just trying to > understand what is the intended usage for the flag that does try to say > more than the madvise status. And moreover, how is the PR_SET_THP_DISABLE any different from the global THP disabled case. Do we want to set all vmas to nh as well? -- Michal Hocko SUSE Labs