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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BA1A5C433F5 for ; Wed, 10 Nov 2021 08:14:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9B5A4610F8 for ; Wed, 10 Nov 2021 08:14:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229582AbhKJIRe (ORCPT ); Wed, 10 Nov 2021 03:17:34 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:54709 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230031AbhKJIRe (ORCPT ); Wed, 10 Nov 2021 03:17:34 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1636532086; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VRNRQyUTnzlLVnEZtE2AkClya4QUFn8/IlNw/XyFTA0=; b=XqOptqSLZ/k6W4kLXIDH6RZKPKVV4P5MT5XLjAS0Ac5W93BF8sQpB+oJMV/DB6a7kRHU04 +wqJGD+PifEcFEOQLbE7ChAddtIYAA29T3ZgmOpVXlkFmdW5kS9SJ1tReIhb8O9BUFPuvR Hu8CtC/asipBzWjNLwqijdjMWEnzvjU= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-16-4O0wk3STPdSOWIrwuGbgVw-1; Wed, 10 Nov 2021 03:14:45 -0500 X-MC-Unique: 4O0wk3STPdSOWIrwuGbgVw-1 Received: by mail-wm1-f72.google.com with SMTP id y9-20020a1c7d09000000b003316e18949bso768861wmc.5 for ; Wed, 10 Nov 2021 00:14:45 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:organization:in-reply-to :content-transfer-encoding; bh=VRNRQyUTnzlLVnEZtE2AkClya4QUFn8/IlNw/XyFTA0=; b=S+a2lHPqIfHYusP3HX/53KkdIySQs7w1qOEtcz2MvXx8/T/bs5klBUwanJ2NnfC8D0 Bn7BfnVB6zFuFWIW5yCBXCPRniRi+BI2egdkW0gvpEaT6DFVjTcv5+IY2iM/1Z6CG95W 3FHdtfVser3YJBUf3A4GQL0L+0nESWFeQdvPxaIjjaoe70GHN8x8YJ2VFxBeb7QRnE7t yZFSyqF1U99pljdFcLurelA2ScHoNg08AAEP+AJwgJ6EJCzyBpbrdDFk9Hce6VYJxOcg uMKt7aF9k4fxRh4Hg9AspZwzS7KHRCaATEp7wnwk6897AUzM0wPiAtW3FkW1JVTTFW8m TEqw== X-Gm-Message-State: AOAM531XoaX+c/ahypXuUGJHgIgmrLeFBLocPKiBJJHR/jR+5eQxzdTh PPq5Kef8PM9OvjozWY0bsWVfSGxt5mJZsHBYQW/TydqNBOgWccqLxlempM+W5jjRRuVvOXsHbLZ 47FlGE8s7fkiuAsKmtJVpXjVN9g== X-Received: by 2002:a5d:584c:: with SMTP id i12mr17905125wrf.95.1636532084434; Wed, 10 Nov 2021 00:14:44 -0800 (PST) X-Google-Smtp-Source: ABdhPJw4dpF+9h8LV87D9pZFz8cxyVWRVQUWPuD6s1mUnxonVBOGF7DYa06GNXlBIp4oI9oYiNDs+Q== X-Received: by 2002:a5d:584c:: with SMTP id i12mr17905107wrf.95.1636532084265; Wed, 10 Nov 2021 00:14:44 -0800 (PST) Received: from [192.168.3.132] (p5b0c604f.dip0.t-ipconnect.de. [91.12.96.79]) by smtp.gmail.com with ESMTPSA id z6sm22659735wrm.93.2021.11.10.00.14.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Nov 2021 00:14:43 -0800 (PST) Message-ID: Date: Wed, 10 Nov 2021 09:14:42 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH v4] mm: Add PM_HUGE_THP_MAPPING to /proc/pid/pagemap Content-Language: en-US To: Peter Xu , Mina Almasry Cc: Matthew Wilcox , "Paul E . McKenney" , Yu Zhao , Jonathan Corbet , Andrew Morton , Ivan Teterevkov , Florian Schmidt , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org References: <20211107235754.1395488-1-almasrymina@google.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 10.11.21 08:03, Peter Xu wrote: > Hi, Mina, > > Sorry to comment late. > > On Sun, Nov 07, 2021 at 03:57:54PM -0800, Mina Almasry wrote: >> diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst >> index fdc19fbc10839..8a0f0064ff336 100644 >> --- a/Documentation/admin-guide/mm/pagemap.rst >> +++ b/Documentation/admin-guide/mm/pagemap.rst >> @@ -23,7 +23,8 @@ There are four components to pagemap: >> * Bit 56 page exclusively mapped (since 4.2) >> * Bit 57 pte is uffd-wp write-protected (since 5.13) (see >> :ref:`Documentation/admin-guide/mm/userfaultfd.rst `) >> - * Bits 57-60 zero >> + * Bit 58 page is a huge (PMD size) THP mapping >> + * Bits 59-60 zero >> * Bit 61 page is file-page or shared-anon (since 3.5) >> * Bit 62 page swapped >> * Bit 63 page present >> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c >> index ad667dbc96f5c..6f1403f83b310 100644 >> --- a/fs/proc/task_mmu.c >> +++ b/fs/proc/task_mmu.c >> @@ -1302,6 +1302,7 @@ struct pagemapread { >> #define PM_SOFT_DIRTY BIT_ULL(55) >> #define PM_MMAP_EXCLUSIVE BIT_ULL(56) >> #define PM_UFFD_WP BIT_ULL(57) >> +#define PM_HUGE_THP_MAPPING BIT_ULL(58) > > The ending "_MAPPING" seems redundant to me, how about just call it "PM_THP" or > "PM_HUGE" (as THP also means HUGE already)? > > IMHO the core problem is about permission controls, and it seems to me we're > actually trying to workaround it by duplicating some information we have.. so > it's kind of a pity. Totally not against this patch, but imho it'll be nicer > if it's the permission part that to be enhanced, rather than a new but slightly > duplicated interface. It's not a permission problem AFAIKS: even with permissions "changed", any attempt to use /proc/kpageflags is just racy. Let's not go down that path, it's really the wrong mechanism to export to random userspace. We do have an interface to access this information from userspace already: /proc/self/smaps IIRC. Mina commented that they are seeing performance issues with that approach. It would be valuable to add these details to the patch description, including a performance difference when using both interfaces we have available. As the patch description stands, there is no explanation "why" we want this change. -- Thanks, David / dhildenb