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=-13.2 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL autolearn=no 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 533CBC433E0 for ; Wed, 23 Dec 2020 04:10:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1B9642231F for ; Wed, 23 Dec 2020 04:10:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726960AbgLWEKJ (ORCPT ); Tue, 22 Dec 2020 23:10:09 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52832 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725938AbgLWEKJ (ORCPT ); Tue, 22 Dec 2020 23:10:09 -0500 Received: from mail-wm1-x330.google.com (mail-wm1-x330.google.com [IPv6:2a00:1450:4864:20::330]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D12FBC0613D3 for ; Tue, 22 Dec 2020 20:09:28 -0800 (PST) Received: by mail-wm1-x330.google.com with SMTP id e25so4964095wme.0 for ; Tue, 22 Dec 2020 20:09:28 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=mEKgkwouOKYZHcH4n91a1kSOJQB4OjAj1Ym6t3oLUZg=; b=GCyHsTtMvVF+o0PPsA9JOPc3Tnap8ECvAQEXYjF1qfaHhpND1UDgZGZY54wH3DSJF9 rWvR5SZg28KD8mt7NHlrhrqiRwCvOF3vWW3jo7RjGssZseK0AouuXu6+RVP4L+SuYKWZ VwOonhik47uTNWOY9g5gfYlYGlbWKunaKQHPKC8Mbv3JpuHIIoBpZaDwBxYYOhsXhDOI zlFxpJ9p1pcGczqiEmYv+1EceIPb+YuY3YEuoUjdlZ9/elsrOxTQP+PPC9m+ha1ARkki tFNJQvtfsq6BAF6GjPP59m139vYLQMPjbS0zyg2Hqp3AV7VEglVdijZYENSyzPnMzQvn GO3Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=mEKgkwouOKYZHcH4n91a1kSOJQB4OjAj1Ym6t3oLUZg=; b=AWQ7u9Vo9TrN2wOKBFoBBfIqn6v74R7juNV4Wo5gA7Vel42IbHJWk9+EudUrnXjj+S IOKBI6KO17Kq6THyWGtFJ1wPy5kOZD7EOV1TFTVMI/yAB8LbYtgGIz5YuJD/78zcsw6J o9HG65/VxUl0FsdRr6uPIXLeVh1+hJ2l5QpW0VYArwmeH1kAkyAPNpYvnoZiCl5OHrrl ME6gwz+y4S6NZgg1P6HZBowJCyFqKKVeDrnBnzI4mlbWpjSJ4x7oHfJBCjC4Sk22OVfQ R0EqxuPeW0aREzvI2uNi8evi7s0XhpGZRd/NWK9lnljYpyCMwCkVBq6vGuCB9a3vq8Kk Jreg== X-Gm-Message-State: AOAM531284rjKmMnzDcAMuUREdGTFIWJbDh6y6y1RAOtIzy1eA+WOafD m623VhSR/+bRz99M5kLxXIv7epa8vwHDDhkdpfoBdw== X-Google-Smtp-Source: ABdhPJxPVdCgx7+QCZCFCNYd3eHZZxJkjYTnkoaSbYlibmLYDpD+CjFqTDwkRlBahO8dCv8H6X9PKIFxzwatSmNQQEk= X-Received: by 2002:a1c:bc57:: with SMTP id m84mr24633253wmf.163.1608696567336; Tue, 22 Dec 2020 20:09:27 -0800 (PST) MIME-Version: 1.0 References: <20201124053943.1684874-1-surenb@google.com> <20201124053943.1684874-2-surenb@google.com> <20201125231322.GF1484898@google.com> <20201222134438.GA7170@infradead.org> In-Reply-To: From: Suren Baghdasaryan Date: Tue, 22 Dec 2020 20:09:16 -0800 Message-ID: Subject: Re: [PATCH 1/2] mm/madvise: allow process_madvise operations on entire memory range To: Christoph Hellwig Cc: Jann Horn , Minchan Kim , Christoph Hellwig , Andrew Morton , Michal Hocko , Michal Hocko , David Rientjes , Matthew Wilcox , Johannes Weiner , Roman Gushchin , Rik van Riel , Christian Brauner , Oleg Nesterov , Tim Murray , Linux API , Linux-MM , kernel list , kernel-team Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Tue, Dec 22, 2020 at 9:48 AM Suren Baghdasaryan wrote: > > On Tue, Dec 22, 2020 at 5:44 AM Christoph Hellwig wrote: > > > > On Fri, Dec 11, 2020 at 09:27:46PM +0100, Jann Horn wrote: > > > > Can we just use one element in iovec to indicate entire address rather > > > > than using up the reserved flags? > > > > > > > > struct iovec { > > > > .iov_base = NULL, > > > > .iov_len = (~(size_t)0), > > > > }; > > > > > > In addition to Suren's objections, I think it's also worth considering > > > how this looks in terms of compat API. If a compat process does > > > process_madvise() on another compat process, it would be specifying > > > the maximum 32-bit number, rather than the maximum 64-bit number, so > > > you'd need special code to catch that case, which would be ugly. > > > > > > And when a compat process uses this API on a non-compat process, it > > > semantically gets really weird: The actual address range covered would > > > be larger than the address range specified. > > > > > > And if we want different access checks for the two flavors in the > > > future, gating that different behavior on special values in the iovec > > > would feel too magical to me. > > > > > > And the length value SIZE_MAX doesn't really make sense anyway because > > > the length of the whole address space would be SIZE_MAX+1, which you > > > can't express. > > > > > > So I'm in favor of a new flag, and strongly against using SIZE_MAX as > > > a magic number here. > > > > Yes, using SIZE_MAX is a horrible interface in this case. I'm not > > a huge fan of a flag either. What is the use case for the madvise > > to all of a processes address space anyway? > > Thanks for the feedback! The use case is userspace memory reaping > similar to oom-reaper. Detailed justification is here: > https://lore.kernel.org/linux-mm/20201124053943.1684874-1-surenb@google.com Actually this post in the most informative and includes test results: https://lore.kernel.org/linux-api/CAJuCfpGz1kPM3G1gZH+09Z7aoWKg05QSAMMisJ7H5MdmRrRhNQ@mail.gmail.com/