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([2a0c:5a80:1204:1500:37e7:8150:d9df:36f]) by smtp.gmail.com with ESMTPSA id z17sm4531039wmf.11.2022.02.09.03.36.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Feb 2022 03:36:04 -0800 (PST) Message-ID: <035d9c7a21eb024e336dce0942fa3f85b864aaea.camel@redhat.com> Subject: Re: [PATCH 0/2] mm/page_alloc: Remote per-cpu lists drain support From: Nicolas Saenz Julienne To: Xiongfeng Wang , akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, frederic@kernel.org, tglx@linutronix.de, mtosatti@redhat.com, mgorman@suse.de, linux-rt-users@vger.kernel.org, vbabka@suse.cz, cl@linux.com, paulmck@kernel.org, willy@infradead.org Date: Wed, 09 Feb 2022 12:36:02 +0100 In-Reply-To: References: <20220208100750.1189808-1-nsaenzju@redhat.com> <7c87f388-cc50-e9a1-17a7-802bb42656e4@huawei.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.42.3 (3.42.3-1.fc35) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2022-02-09 at 19:26 +0800, Xiongfeng Wang wrote: > Hi, > > On 2022/2/9 17:45, Nicolas Saenz Julienne wrote: > > Hi Xiongfeng, thanks for taking the time to look at this. > > > > On Wed, 2022-02-09 at 16:55 +0800, Xiongfeng Wang wrote: > > > Hi Nicolas， > > > > > > When I applied the patchset on the following commit and tested on QEMU, I came > > > accross the following CallTrace. > > > commit dd81e1c7d5fb126e5fbc5c9e334d7b3ec29a16a0 > > > > > > I wrote a userspace application to consume the memory. When the memory is used > > > out, the OOM killer is triggered and the following Calltrace is printed. I am > > > not sure if it is related to this patchset. But when I reverted this patchset, > > > the 'NULL pointer' Calltrace didn't show. > > > > It's a silly mistake on my part, while cleaning up the code I messed up one of > > the 'struct per_cpu_pages' accessors. This should fix it: > > > > ------------------------->8------------------------- > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 0caa7155ca34..e65b991c3dc8 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -3279,7 +3279,7 @@ static void __drain_all_pages(struct zone *zone, bool force_all_cpus) > > has_pcps = true; > > } else { > > for_each_populated_zone(z) { > > - pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu); > > + pcp = per_cpu_ptr(z->per_cpu_pageset, cpu); > > lp = rcu_dereference_protected(pcp->lp, > > mutex_is_locked(&pcpu_drain_mutex)); > > if (lp->count) { > > I have tested it. It works well. No more 'NULL pointer' Calltrace. Thanks! -- Nicolás Sáenz