Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753786Ab0KJB23 (ORCPT ); Tue, 9 Nov 2010 20:28:29 -0500 Received: from smtp-out.google.com ([216.239.44.51]:4962 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751418Ab0KJB22 (ORCPT ); Tue, 9 Nov 2010 20:28:28 -0500 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=from:to:cc:subject:references:date:in-reply-to:message-id: user-agent:mime-version:content-type; b=illHNCvRXzH8QmwRfEiCNCXQkz4JolzXGcCvprweliO+AxhxLALJEbbQxnnoVXM6s 2o/WEfMNgozgCfgPTk0Kg== From: Greg Thelen To: David Rientjes Cc: Johannes Weiner , Andrew Morton , KAMEZAWA Hiroyuki , Balbir Singh , Daisuke Nishimura , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: mem_cgroup_get_limit() return type, was [patch] memcg: fix unit mismatch in memcg oom limit calculation References: <20101109110521.GS23393@cmpxchg.org> Date: Tue, 09 Nov 2010 17:26:34 -0800 In-Reply-To: (David Rientjes's message of "Tue, 9 Nov 2010 15:21:50 -0800 (PST)") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2050 Lines: 49 David Rientjes writes: > On Tue, 9 Nov 2010, Greg Thelen wrote: > >> >> > Adding the number of swap pages to the byte limit of a memory control >> >> > group makes no sense. Convert the pages to bytes before adding them. >> >> > >> >> > The only user of this code is the OOM killer, and the way it is used >> >> > means that the error results in a higher OOM badness value. Since the >> >> > cgroup limit is the same for all tasks in the cgroup, the error should >> >> > have no practical impact at the moment. >> >> > >> >> > But let's not wait for future or changing users to trip over it. >> >> >> >> Thanks for the fix. >> >> >> > >> > Nice catch, but it's done in the opposite way: the oom killer doesn't use >> > byte limits but page limits. So this needs to be >> > >> > (res_counter_read_u64(&memcg->res, RES_LIMIT) >> PAGE_SHIFT) + >> > total_swap_pages; >> >> In -mm, the oom killer queries memcg for a byte limit using >> mem_cgroup_get_limit(). The following is from >> mem_cgroup_out_of_memory(): >> >> limit = mem_cgroup_get_limit(mem) >> PAGE_SHIFT; >> > > Oops, I missed that. I think Johannes' patch is better because > mem_cgroup_get_limit() may eventually be used elsewhere and the subsystem > has byte granularity. I have no problem with mem_cgroup_get_limit() returning a byte count as you prefer. I think this approach does have an issue. "mem_cgroup_get_limit() >> PAGE_SHIFT" may not fit within unsigned long on 32-bit machines. Does this cause a problem for the 'limit' local variable in mem_cgroup_out_of_memory(): limit = mem_cgroup_get_limit(mem) >> PAGE_SHIFT; Do we need something like the following in mem_cgroup_out_of_memory() to guard against this overflow? limit = min(mem_cgroup_get_limit(mem) >> PAGE_SHIFT, ULONG_MAX); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/