From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 437066B0007 for ; Wed, 17 Oct 2018 03:05:34 -0400 (EDT) Received: by mail-ed1-f70.google.com with SMTP id g36-v6so16140807edb.3 for ; Wed, 17 Oct 2018 00:05:34 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id q23-v6si5226579edg.419.2018.10.17.00.05.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 17 Oct 2018 00:05:32 -0700 (PDT) Date: Wed, 17 Oct 2018 09:05:31 +0200 From: Michal Hocko Subject: Re: [RFC PATCH] mm, proc: report PR_SET_THP_DISABLE in proc Message-ID: <20181017070531.GC18839@dhcp22.suse.cz> References: <20181004055842.GA22173@dhcp22.suse.cz> <20181004094637.GG22173@dhcp22.suse.cz> <20181009083326.GG8528@dhcp22.suse.cz> <20181015150325.GN18839@dhcp22.suse.cz> <20181016104855.GQ18839@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: 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 On Tue 16-10-18 14:24:19, David Rientjes wrote: > On Tue, 16 Oct 2018, Michal Hocko wrote: > > > > I don't understand the point of extending smaps with yet another line. > > > > Because abusing a vma flag part is just wrong. What are you going to do > > when a next bug report states that the flag is set even though no > > userspace has set it and that leads to some malfunctioning? Can you rule > > that out? Even your abuse of the flag is surprising so why others > > wouldn't be? > > > > The flag has taken on the meaning of "thp disabled for this vma", how it > is set is not the scope of the flag. If a thp is explicitly disabled from > being eligible for thp, whether by madvise, prctl, or any future > mechanism, it should use VM_NOHUGEPAGE or show_smap_vma_flags() needs to > be modified. No, this is not the meaning which is documented nh - no-huge page advise flag and as far as I know it is only you who has complained so far. > > As I've said there are two things. Exporting PR_SET_THP_DISABLE to > > userspace so that a 3rd party process can query it. I've already > > explained why that might be useful. If you really insist on having > > a per-vma field then let's do it properly now. Are you going to agree on > > that? If yes, I am willing to spend my time on that but I am not going > > to bother if this will lead to "I want my vma field abuse anyway". > > I think what you and I want is largely irrelevant :) What's important is > that there are userspace implementations that query this today so > continuing to support it as the way to determine if a vma has been thp > disabled doesn't seem problematic and guarantees that userspace doesn't > break. Do you know of any other userspace except your usecase? Is there anything fundamental that would prevent a proper API adoption for you? -- Michal Hocko SUSE Labs