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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 01E78C3F2D1 for ; Wed, 4 Mar 2020 16:39:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C69E22166E for ; Wed, 4 Mar 2020 16:39:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583339966; bh=SuMPqA4YEWLeVNaCMC8pfhG2ZR/Km0sO+0l7v9BDf2I=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=UlNNnifxZqAp+Ia2GH2CvAdPY/8OTl20fKbgPTI94h6zSowTJqPs5GjnejyI52Wr0 gOKLBvuHDUdsYVTO4Ai+fijJ4Ynmt7bHfloucOrpEb8nTy/xl5MZEBPmMKTl31bxN4 JaLOb6O1mMOuzlPleOz7BpNCMiJUvSD5nN1JwAiY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729875AbgCDQjZ (ORCPT ); Wed, 4 Mar 2020 11:39:25 -0500 Received: from mail-qt1-f194.google.com ([209.85.160.194]:36446 "EHLO mail-qt1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729689AbgCDQjZ (ORCPT ); Wed, 4 Mar 2020 11:39:25 -0500 Received: by mail-qt1-f194.google.com with SMTP id t13so1841572qto.3; Wed, 04 Mar 2020 08:39:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=Q41tiblFE54JAr5vC6itpkRF9zh1xfIn6lFKVFQ8hPE=; b=jgpGs27cukeF4u6jimr8YXOzqdUGDnBvlaasW3APkR/3ylULaFPdFft2i7tjdKMoug K6v0nKjw50uodI+joOgqp920D8ANct5b0St90yLhBMiPOSfBrwMO9U+phnqmFMuzglpg 884HqvfXDMjsXb50UTyzG34uXIQ9eJS65e+7fP2KA5Irn35utXNDG9ekv2KX/eIEX7gQ a04loJYII0g/hCdWfBKxsGrEygu86tSmz6TSKkuydhhucErZcw0NdksFDxA1hMOXyQ6E deVaNCkiC1C/Oli/G4zom94cs+cxd+ivOZIY2MGkg3jUkAjZQ8LR7OXBXHkOao9nR4y8 pTIQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=Q41tiblFE54JAr5vC6itpkRF9zh1xfIn6lFKVFQ8hPE=; b=YVf2OU0VHl4IFnpEn9Zw6W8eTH4JdWYPlkLXKXpAZxTbt4I5wAIjZEYv0Qvhn0aAaP gJ+EqpXZbmC2u/3AtY71PQsb1PbG2w+H/n+g9xRKypCnUSKjJ3dxY0UwWl3OKvVnXBZx wdvVze1wGjY/b5sNQTKPhz/zTO1Vg9uVgav/UZLMueYy0+wEJhtPQeXOglSh6VWCd7hH KcK91Yp6HQSZwx5ihtbdl8cGQ9YHcMyg2gUJi1x2T17PvXrM9R+BTH6mb/mn+ZKZPe6d vg6za9tqhjC6/nC7HTMJ5mpV9NQtNPxQbWdlyKczrRWvAYnCJF3+OVnw7B1VKOyImXw6 ckmg== X-Gm-Message-State: ANhLgQ3QakZem5zRdZWgIlNe6+tUbrDNxkXcHB+tTFsfdc+EtFFYvUcW on5ZtWQ3Rsdz0vT01XjQQdS1j7mnC/A= X-Google-Smtp-Source: ADFU+vv6B6uHErWbe6EYCVm4UjJigrIY9oE2hn3aI/w5O4AOCgONkkVZPGldpOis+jjjZWdPotLDnA== X-Received: by 2002:ac8:e45:: with SMTP id j5mr117129qti.215.1583339964277; Wed, 04 Mar 2020 08:39:24 -0800 (PST) Received: from localhost ([71.172.127.161]) by smtp.gmail.com with ESMTPSA id d1sm1903151qtn.78.2020.03.04.08.39.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Mar 2020 08:39:23 -0800 (PST) Date: Wed, 4 Mar 2020 11:39:22 -0500 From: Tejun Heo To: Daniel Xu Cc: cgroups@vger.kernel.org, lizefan@huawei.com, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org, kernel-team@fb.com Subject: Re: [PATCH 1/2] kernfs: Add option to enable user xattrs Message-ID: <20200304163922.GG189690@mtj.thefacebook.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Tue, Mar 03, 2020 at 11:37:28AM -0800, Daniel Xu wrote: > It looks like in fs/xattr.c:setxattr, there is already: > > ... > if (size) { > if (size > XATTR_SIZE_MAX) > return -E2BIG; > ... > > where XATTR_SIZE_MAX is defined as 64k. Do you want it even smaller? Oh, I missed that. Order 5 allocations can still be on the big side tho. Ideally, something like the following? * Total number of bytes limit as the primary limit so that we can say that for a given cgroup user xattrs don't consume more than X bytes. We can pick an arbitrary number which is large enough for most use cases but not too big. e.g. 128k or whatever. * Total number of xattrs limit. Again, some arbitrary not too low, not too high limit. * Switch to kvmalloc() for attr allocation so that we don't have to worry about high order allocations. Thanks. -- tejun