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Fri, 13 Nov 2026 16:03:25 -0800 (PST) Received: from localhost ([2a03:2880:10ff:5e::]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-67d8a4359absm3414111d50.1.2026.11.13.16.03.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Nov 2026 16:03:24 -0800 (PST) Date: Fri, 13 Nov 2026 16:03:24 -0800 From: Joshua Hahn To: "Gregory Price (Meta)" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, david@kernel.org, ziy@nvidia.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com Subject: Re: [PATCH] mm/mempolicy: ignore a bind policy whose nodes have no memory Message-ID: Mail-Followup-To: "Gregory Price (Meta)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, david@kernel.org, ziy@nvidia.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com References: <20261113192642.2618878-1-gourry@gourry.net> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261113192642.2618878-1-gourry@gourry.net> On Fri, Nov 13, 2026 at 02:26:42PM -0500, Gregory Price (Meta) wrote: > apply_policy_zone() assumes that policy->nodes intersects N_MEMORY, so > it reads a bind policy with no N_HIGH_MEMORY node as movable-only. > > On systems with CONFIG_CPUSETS=n, nothing rebinds policies when memory > is removed, so offlining all memory on the nodes a bind policy names > leaves it with none. The policy is then treated as movable-only, and > movable allocations are restricted to nodes without memory. > > This results in allocations failures, a VM_FAULT_OOM leak, and then > an infinitely retrying fault that hangs the process. > > page allocation failure: order:0, mode:0x140dca ... nodemask=2 > Huh VM_FAULT_OOM leaked out to the #PF handler. Retrying PF > > Ignore a bind policy whose nodes have no memory. policy_nodemask() > already ignores a bind policy that does not intersect the cpuset. > This covers hugetlb's policy_mbind_nodemask() as well. > > If the nodes regain memory, the policy applies again. > > CPUSETS=n with HOTREMOVE=y is unlikely a common configuration, so this > isn't marked for stable. > > Signed-off-by: Gregory Price (Meta) Hello Gregory, Cool find! Thanks for fixing this. Reviewed-by: Joshua Hahn > --- > mm/mempolicy.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index ca7e744727b1..5dc2d7ef1544 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -2096,6 +2096,10 @@ bool apply_policy_zone(struct mempolicy *policy, enum zone_type zone) > > BUG_ON(dynamic_policy_zone == ZONE_MOVABLE); > > + /* Memory hot-remove can leave policy->nodes without memory. */ > + if (!nodes_intersects(policy->nodes, node_states[N_MEMORY])) > + return false; > + > /* > * if policy->nodes has movable memory only, > * we apply policy when gfp_zone(gfp) = ZONE_MOVABLE only. > -- > 2.56.0 >