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=-14.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 C1409C433DB for ; Sat, 13 Feb 2021 22:04:30 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 155AB64E43 for ; Sat, 13 Feb 2021 22:04:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 155AB64E43 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 7B3378D00CC; Sat, 13 Feb 2021 17:04:29 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 763298D0060; Sat, 13 Feb 2021 17:04:29 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 652698D00CC; Sat, 13 Feb 2021 17:04:29 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0251.hostedemail.com [216.40.44.251]) by kanga.kvack.org (Postfix) with ESMTP id 4D73C8D0060 for ; Sat, 13 Feb 2021 17:04:29 -0500 (EST) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 178C0812D for ; Sat, 13 Feb 2021 22:04:29 +0000 (UTC) X-FDA: 77814624258.16.taste40_01147bc2762d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin16.hostedemail.com (Postfix) with ESMTP id EA2F2100E690B for ; Sat, 13 Feb 2021 22:04:28 +0000 (UTC) X-HE-Tag: taste40_01147bc2762d X-Filterd-Recvd-Size: 9809 Received: from mail-wr1-f50.google.com (mail-wr1-f50.google.com [209.85.221.50]) by imf47.hostedemail.com (Postfix) with ESMTP for ; Sat, 13 Feb 2021 22:04:28 +0000 (UTC) Received: by mail-wr1-f50.google.com with SMTP id u14so4199824wri.3 for ; Sat, 13 Feb 2021 14:04:28 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=cc:subject:to:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=8QdWTAJ+beg12quntIhZalfc07GrzP+2YyUm2HopaRE=; b=SDV1e/8p0mhz8BYGtaU8iXpVNnzGc/lsF99FH6PlV6Frz34BSC/wr9tOlTwd5C3qKN JpRnsYIYL1Y0dZLvlX078YM39xoN9Zp9XL+23x8RfR0tB2LrlPgEnUncmxTDqM59VTQA kmBF8JAxAXOGfDFGE9DLJ/fLJQdVFU6kyWA+Sk/WLWIuNal/oijtFn/7nI9ZAbD2qO8K f9a5muDX+ywFF9T/Paz2QiKGuVCRuIcEVB+1/kZEhJyKA5ua4EJtAJ+0Qv0RiaKZ4Ko0 zq6al7Wa/ITyzyz3bDJcRhEbBgCy326AtHgR5u4snp9eCx1/cmImE4iHi8ovwUkNPsNC GGoQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:cc:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=8QdWTAJ+beg12quntIhZalfc07GrzP+2YyUm2HopaRE=; b=tHV3bcpXLL/VqmsRzndkRgotmoM0mkWViEO4AtcIr0oTzL36wLJkraqS8x2Z6i3veE I/x1+byCIWwXGZa74gWrxig02LXzprqtxpbSiuV3IM1WVBxDhpkkGVgK/Wj52IhRN7Iq GhXzeACr6Y+53MuunlIVBQ3mIbJE3teglgeXSWGBXHx27fFcmPY9H8mwyv3Tzf+jJzjE OYrdEtKR7F/w4HMYxOXsGAZ/J7tJLOLgc90ZODQ6JP4wWatv50l1vLTFqz5Z8NPdVEJL Mn5FDcB7RHCMqw0tRRD2KU2LjGTLD+Ww1Xi4kpqRTida6r+8Y7YzWxajkX7G0nmZCFON B5OA== X-Gm-Message-State: AOAM533q4FPCjP/4pKR610EX/Y4ePmStJiv8M+bFrLkvM4Q2/f1f/fEU H1ecJw8hXlbitJBkRT5PtZQ= X-Google-Smtp-Source: ABdhPJyK3AQIsJbi2V5mWgsIJwWnJfg9UssexqDTKfiEhKzTFbke9lDM1hFwoWdxJRbg6g+V5Or4sA== X-Received: by 2002:adf:ef86:: with SMTP id d6mr6449258wro.419.1613253867076; Sat, 13 Feb 2021 14:04:27 -0800 (PST) Received: from ?IPv6:2001:a61:3a2d:1d01:99ab:4f20:ed7f:402b? ([2001:a61:3a2d:1d01:99ab:4f20:ed7f:402b]) by smtp.gmail.com with ESMTPSA id o18sm17971832wmp.19.2021.02.13.14.04.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 13 Feb 2021 14:04:26 -0800 (PST) Cc: mtk.manpages@gmail.com, linux-man , Andrew Morton , Jann Horn , Kees Cook , Jeffrey Vander Stoep , Minchan Kim , Michal Hocko , Shakeel Butt , David Rientjes , =?UTF-8?Q?Edgar_Arriaga_Garc=c3=ada?= , Tim Murray , linux-mm , SElinux list , linux-security-module , Linux API , LKML , kernel-team Subject: Re: [PATCH v3 1/1] process_madvise.2: Add process_madvise man page To: Suren Baghdasaryan References: <20210202053046.1653012-1-surenb@google.com> <079db245-a08c-0dbd-01d4-8065f533652e@gmail.com> From: "Michael Kerrisk (man-pages)" Message-ID: <2d303517-cdcd-9ec8-e57d-3d065edb573c@gmail.com> Date: Sat, 13 Feb 2021 23:04:23 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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: Hello Suren, On 2/2/21 11:12 PM, Suren Baghdasaryan wrote: > Hi Michael, > > On Tue, Feb 2, 2021 at 2:45 AM Michael Kerrisk (man-pages) > wrote: >> >> Hello Suren (and Minchan and Michal) >> >> Thank you for the revisions! >> >> I've applied this patch, and done a few light edits. > > Thanks! > >> >> However, I have a questions about undocumented pieces in *madvise(2)*, >> as well as one other question. See below. >> >> On 2/2/21 6:30 AM, Suren Baghdasaryan wrote: >>> Initial version of process_madvise(2) manual page. Initial text was >>> extracted from [1], amended after fix [2] and more details added using >>> man pages of madvise(2) and process_vm_read(2) as examples. It also >>> includes the changes to required permission proposed in [3]. >>> >>> [1] https://lore.kernel.org/patchwork/patch/1297933/ >>> [2] https://lkml.org/lkml/2020/12/8/1282 >>> [3] https://patchwork.kernel.org/project/selinux/patch/20210111170622.2613577-1-surenb@google.com/#23888311 >>> >>> Signed-off-by: Suren Baghdasaryan >>> Reviewed-by: Michal Hocko >>> --- >>> changes in v2: >>> - Changed description of MADV_COLD per Michal Hocko's suggestion >>> - Applied fixes suggested by Michael Kerrisk >>> changes in v3: >>> - Added Michal's Reviewed-by >>> - Applied additional fixes suggested by Michael Kerrisk >>> >>> NAME >>> process_madvise - give advice about use of memory to a process >>> >>> SYNOPSIS >>> #include >>> >>> ssize_t process_madvise(int pidfd, >>> const struct iovec *iovec, >>> unsigned long vlen, >>> int advice, >>> unsigned int flags); >>> >>> DESCRIPTION >>> The process_madvise() system call is used to give advice or directions >>> to the kernel about the address ranges of another process or the calling >>> process. It provides the advice to the address ranges described by iovec >>> and vlen. The goal of such advice is to improve system or application >>> performance. >>> >>> The pidfd argument is a PID file descriptor (see pidfd_open(2)) that >>> specifies the process to which the advice is to be applied. >>> >>> The pointer iovec points to an array of iovec structures, defined in >>> as: >>> >>> struct iovec { >>> void *iov_base; /* Starting address */ >>> size_t iov_len; /* Number of bytes to transfer */ >>> }; >>> >>> The iovec structure describes address ranges beginning at iov_base address >>> and with the size of iov_len bytes. >>> >>> The vlen represents the number of elements in the iovec structure. >>> >>> The advice argument is one of the values listed below. >>> >>> Linux-specific advice values >>> The following Linux-specific advice values have no counterparts in the >>> POSIX-specified posix_madvise(3), and may or may not have counterparts >>> in the madvise(2) interface available on other implementations. >>> >>> MADV_COLD (since Linux 5.4.1) >> >> I just noticed these version numbers now, and thought: they can't be >> right (because the system call appeared only in v5.11). So I removed >> them. But, of course in another sense the version numbers are (nearly) >> right, since these advice values were added for madvise(2) in Linux 5.4. >> However, they are not documented in the madvise(2) manual page. Is it >> correct to assume that MADV_COLD and MADV_PAGEOUT have exactly the same >> meaning in madvise(2) (but just for the calling process, of course)? > > Correct. They should be added in the madvise(2) man page as well IMHO. So, I decided to move the description of MADV_COLD and MADV_PAGEOUT to madvise(2) and refer to that page from the process_madvise(2) page. This avoids repeating the same information in two places. >>> Deactive a given range of pages which will make them a more probable >> >> I changed: s/Deactive/Deactivate/ > > thanks! > >> >>> reclaim target should there be a memory pressure. This is a >>> nondestructive operation. The advice might be ignored for some pages >>> in the range when it is not applicable. >>> >>> MADV_PAGEOUT (since Linux 5.4.1) >>> Reclaim a given range of pages. This is done to free up memory occupied >>> by these pages. If a page is anonymous it will be swapped out. If a >>> page is file-backed and dirty it will be written back to the backing >>> storage. The advice might be ignored for some pages in the range when >>> it is not applicable. >> >> [...] >> >>> The hint might be applied to a part of iovec if one of its elements points >>> to an invalid memory region in the remote process. No further elements will >>> be processed beyond that point. >> >> Is the above scenario the one that leads to the partial advice case described in >> RETURN VALUE? If yes, perhaps I should add some words to make that clearer. > > Correct. This describes the case when partial advice happens. Thanks. I added a few words to clarify this. >> You can see the light edits that I made in >> https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=e3ce016472a1b3ec5dffdeb23c98b9fef618a97b >> and following that I restructured DESCRIPTION a little in >> https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=3aac0708a9acee5283e091461de6a8410bc921a6 > > The edits LGTM. Thanks for checking them. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/