From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guenter Roeck Subject: Re: mmotm 2015-01-22-15-04: qemu failure due to 'mm: memcontrol: remove unnecessary soft limit tree node test' Date: Fri, 23 Jan 2015 18:02:29 -0800 Message-ID: <54C2FD35.9070803@roeck-us.net> References: <54c1822d.RtdGfWPekQVAw8Ly%akpm@linux-foundation.org> <20150123050802.GB22751@roeck-us.net> <20150123141817.GA22926@phnom.home.cmpxchg.org> <20150123160204.GA32592@phnom.home.cmpxchg.org> <54C27E07.6000908@roeck-us.net> <20150123173659.GB12036@phnom.home.cmpxchg.org> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: Christoph Lameter , akpm@linux-foundation.org, mm-commits@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-next@vger.kernel.org, Stephen Rothwell , mhocko@suse.cz To: Johannes Weiner Return-path: In-Reply-To: <20150123173659.GB12036@phnom.home.cmpxchg.org> Sender: linux-next-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On 01/23/2015 09:36 AM, Johannes Weiner wrote: > On Fri, Jan 23, 2015 at 08:59:51AM -0800, Guenter Roeck wrote: >> On 01/23/2015 08:02 AM, Johannes Weiner wrote: >>> On Fri, Jan 23, 2015 at 09:17:44AM -0600, Christoph Lameter wrote: >>>> On Fri, 23 Jan 2015, Johannes Weiner wrote: >>>> >>>>> Is the assumption of this patch wrong? Does the specified node have >>>>> to be online for the fallback to work? >>>> >>>> Nodes that are offline have no control structures allocated and thus >>>> allocations will likely segfault when the address of the controls >>>> structure for the node is accessed. >>>> >>>> If we wanted to prevent that then every allocation would have to add a >>>> check to see if the nodes are online which would impact performance. >>> >>> Okay, that makes sense, thank you. >>> >>> Andrew, can you please drop this patch? >>> >> Problem is that there are three patches. >> >> 2537ffb mm: memcontrol: consolidate swap controller code >> 2f9b346 mm: memcontrol: consolidate memory controller initialization >> a40d0d2 mm: memcontrol: remove unnecessary soft limit tree node test >> >> Reverting (or dropping) a40d0d2 alone is not possible since it modifies >> mem_cgroup_soft_limit_tree_init which is removed by 2f9b346. > > ("mm: memcontrol: consolidate swap controller code") gave me no issues > when rebasing, but ("mm: memcontrol: consolidate memory controller > initialization") needs updating. > > So how about this one to replace ("mm: memcontrol: remove unnecessary > soft limit tree node test"): > > --- > From: Johannes Weiner > Subject: [patch] mm: memcontrol: simplify soft limit tree init code > > - No need to test the node for N_MEMORY. node_online() is enough for > node fallback to work in slab, use NUMA_NO_NODE for everything else. > > - Remove the BUG_ON() for allocation failure. A NULL pointer crash is > just as descriptive, and the absent return value check is obvious. > > - Move local variables to the inner-most blocks. > > - Point to the tree structure after its initialized, not before, it's > just more logical that way. > > Signed-off-by: Johannes Weiner The latest version in mmotm passes my ppc64 qemu test, so it works at least in this context. Tested-by: Guenter Roeck