From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id E8E676B025F for ; Fri, 20 Oct 2017 02:47:20 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id o44so5298147wrf.0 for ; Thu, 19 Oct 2017 23:47:20 -0700 (PDT) Received: from szxga05-in.huawei.com (szxga05-in.huawei.com. [45.249.212.191]) by mx.google.com with ESMTPS id m125si393723wma.246.2017.10.19.23.47.17 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 19 Oct 2017 23:47:19 -0700 (PDT) Subject: Re: [PATCH] mm/mempolicy: add node_empty check in SYSC_migrate_pages References: <1508290660-60619-1-git-send-email-xieyisheng1@huawei.com> <7086c6ea-b721-684e-fe3d-ff59ae1d78ed@suse.cz> <20aac66a-7252-947c-355b-6da4be671dcf@huawei.com> From: Yisheng Xie Message-ID: <79f20d60-dd8d-2545-5a9b-09871ad8ee4e@huawei.com> Date: Fri, 20 Oct 2017 14:42:38 +0800 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka , akpm@linux-foundation.org, mhocko@suse.com, mingo@kernel.org, rientjes@google.com, n-horiguchi@ah.jp.nec.com, salls@cs.ucsb.edu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, will.deacon@arm.com, tanxiaojun@huawei.com, Linux API Hi Vlastimil, Thanks for your comment! On 2017/10/18 18:46, Vlastimil Babka wrote: > On 10/18/2017 11:34 AM, Yisheng Xie wrote: >>>> For MAX_NUMNODES is 4, so 0x10 nodemask will tread as empty set which makes >>>> nodes_subset(*new, node_states[N_MEMORY]) >>> >>> According to manpage of migrate_pages: >>> >>> EINVAL The value specified by maxnode exceeds a kernel-imposed >>> limit. Or, old_nodes or new_nodes specifies one or more node IDs that >>> are greater than the maximum supported node ID. Or, none of the node >>> IDs specified by new_nodes are on-line and allowed by the process's >>> current cpuset context, or none of the specified nodes contain memory. >>> >>> if maxnode parameter is 64, but MAX_NUMNODES ("kernel-imposed limit") is >>> 4, we should get EINVAL just because of that. I don't see such check in >>> the migrate_pages implementation though. >> >> Yes, that is what manpage said, but I have a question about this: if user >> set maxnode exceeds a kernel-imposed and try to access node without enough >> privilege, which errors values we should return ? For I have seen that all >> of the ltp migrate_pages01 will set maxnode to 64 in my system. > > Hm I don't think it matters much and don't know if there's some commonly > used priority. Personally I would do the checks resulting in EINVAL > first, before EPERM, but if the code is structured differently, it may > stay as it is. I seei 1/4 ?and I have checked the code of get_nodes, which seems treat "kernel-imposed limit" as the meaning of BITS_PER_LONG * BITS_TO_LONGS(MAX_NUMNODES) instead of MAX_NUMNODES, which I have replied in another mail. As we use unsigned long to store node bitmap, so the limit should be counted in multiple of BITS_PER_LONG, fair? Thanks Yisheng Xie -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org