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 D759FC433FE for ; Tue, 5 Oct 2021 19:15:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BDF8361409 for ; Tue, 5 Oct 2021 19:15:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234964AbhJETRE (ORCPT ); Tue, 5 Oct 2021 15:17:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56328 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232861AbhJETRC (ORCPT ); Tue, 5 Oct 2021 15:17:02 -0400 Received: from mail-yb1-xb2c.google.com (mail-yb1-xb2c.google.com [IPv6:2607:f8b0:4864:20::b2c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C2401C06174E for ; Tue, 5 Oct 2021 12:15:11 -0700 (PDT) Received: by mail-yb1-xb2c.google.com with SMTP id s4so29937ybs.8 for ; Tue, 05 Oct 2021 12:15:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Y/mJ1wrJl0e2S4EbithBXePxqkT5yOeu8iCmqxY+6zM=; b=M1kis41L+W8a3X4xSlCWbuPFyHGcq4qAALLCMn7eMkW+D55940o+GnlKZhYo7SfEFf eKx6U0ezgxMJKf89ERCwNbfcEjqSrgI8bXetehSKbTq3hBALUwCIZPjkpgB+cjunVdCS WUOM7tVLgucnzyc8N7gK6PqKOxIpKi31m9jpvL6Suhi3ntBbP04Ksv5mHZBiqQ5gDMuB mlnsP6U61UcL/L4VlXu/rhMogaYmgD7B9TYlwJp7ET39MVF2lwNWW/NYA9HVlvbQWWyg +U9pskA/P247x4+EuPoUg8wGV/hMoaBW2hCKqC5njS/cSZCbY21y0BxIUGtwBZcfJF1H 84mA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Y/mJ1wrJl0e2S4EbithBXePxqkT5yOeu8iCmqxY+6zM=; b=YPrJFxFLPAMxtK1b3RqFIFRn1OZrNrlOtpbfnAQvjdMEyZr+KzENGDUF51AoqSg99J CT61NXApmv8X4+Knc4NiRRzgunwdGJC730Cj9AYGQRnor5Pmdz9ufN70uQFLRLJ/03Ho eu9CPwaqwIthYWK5/8obTrmPqWWJLOzpnh6ogzf39/RMN37jbczXiZPtuK6JBaGp2Ors TWghQ6f51G/fXcyT/i4+qUMkuDNGTYhVOgydeLGlSlzEcCShRSgeNqOUl7XvqZjFQ3O5 3Gy1956dQv5VIa5A08/468FkBs3RCSfVxqY1wtxm2o4SGldKRerxW72RdhgPhIp/R+3g oNUg== X-Gm-Message-State: AOAM531vsdlZYcyVkZIQUL2kdugxM3ks6I7nwCkyxYjbIVUCv23V4Cqw 0hPfTPIyNCAOJk9cYBUmRV6d84IAO7bYYVA+g667Hw== X-Google-Smtp-Source: ABdhPJxa45KExZ/7k/RCApHcxypXu8XAAvYJq3w4XtzePMFBwOXwgWrUVZ+OKZLOGNg4W5UYgNh720duxvdX3NBhPKs= X-Received: by 2002:a25:5646:: with SMTP id k67mr25382729ybb.127.1633461310475; Tue, 05 Oct 2021 12:15:10 -0700 (PDT) MIME-Version: 1.0 References: <20211001205657.815551-1-surenb@google.com> <20211001205657.815551-3-surenb@google.com> <20211005184211.GA19804@duo.ucw.cz> In-Reply-To: <20211005184211.GA19804@duo.ucw.cz> From: Suren Baghdasaryan Date: Tue, 5 Oct 2021 12:14:59 -0700 Message-ID: Subject: Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting To: Pavel Machek Cc: Andrew Morton , Colin Cross , Sumit Semwal , Michal Hocko , Dave Hansen , Kees Cook , Matthew Wilcox , "Kirill A . Shutemov" , Vlastimil Babka , Johannes Weiner , Jonathan Corbet , Al Viro , Randy Dunlap , Kalesh Singh , Peter Xu , rppt@kernel.org, Peter Zijlstra , Catalin Marinas , vincenzo.frascino@arm.com, =?UTF-8?B?Q2hpbndlbiBDaGFuZyAo5by16Yym5paHKQ==?= , Axel Rasmussen , Andrea Arcangeli , Jann Horn , apopple@nvidia.com, John Hubbard , Yu Zhao , Will Deacon , fenghua.yu@intel.com, thunder.leizhen@huawei.com, Hugh Dickins , feng.tang@intel.com, Jason Gunthorpe , Roman Gushchin , Thomas Gleixner , krisman@collabora.com, chris.hyser@oracle.com, Peter Collingbourne , "Eric W. Biederman" , Jens Axboe , legion@kernel.org, Rolf Eike Beer , Cyrill Gorcunov , Muchun Song , Viresh Kumar , Thomas Cedeno , sashal@kernel.org, cxfcosmos@gmail.com, Rasmus Villemoes , LKML , linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm , kernel-team Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Tue, Oct 5, 2021 at 11:42 AM Pavel Machek wrote: > > On Fri 2021-10-01 13:56:57, Suren Baghdasaryan wrote: > > While forking a process with high number (64K) of named anonymous vmas the > > overhead caused by strdup() is noticeable. Experiments with ARM64 > Android > > I still believe you should simply use numbers and do the > numbers->strings mapping in userspace. We should not need to optimize > strdups in kernel... Here are complications with mapping numbers to strings in the userspace: Approach 1: hardcode number->string in some header file and let all tools use that mapping. The issue is that whenever that mapping changes all the tools that are using it (including 3rd party ones) have to be rebuilt. This is not really maintainable since we don't control 3rd party tools and even for the ones we control, it will be a maintenance issue figuring out which version of the tool used which header file. Approach 2: have a centralized facility (a process or a DB) maintaining number->string mapping. This would require an additional request to this facility whenever we want to make a number->string conversion. Moreover, when we want to name a VMA, we would have to register a new VMA name in that facility or check that one already exists and get its ID. So each prctl() call to name a VMA will be preceded by such a request (IPC call), maybe with some optimizations to cache already known number->string pairs. This would be quite expensive performance-wise. Additional issue with this approach is that this mapping will have to be persistent to handle a case when the facility crashes and has to be restored. As I said before, it complicates userspace quite a bit. Is that a good enough reason to store the names in the kernel and pay a little more memory for that? IMHO yes, but I might be wrong. Thanks, Suren. > > Best regards, > Pavel > -- > http://www.livejournal.com/~pavelmachek > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com.