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b=c/cVKUWwvHQlXN8u4cB6G6LD5VOsTXkW1mYttiSFtfYQOC8o6gttQiR/PM29yMxre retigVXoKJ0F5JJV4gU29i4c5I8lxwG24QQOku1iOAaPHnINtOyviaNmPdB3cihQ+r wplgUCifRTKChtG7AS25gs2Cc31HDdxs+utyIqtN6UWTL+Su+Hg4DWIuUuz3tdvk37 S6dAoU+2qxiJBWwT3CkJPokw3/yMy5yTf2Bo4s9TqXC3MNAGSmNypMdYE/dcdJxfMW rUzy71vmkFD+RmCUeyTTEUPa/4Y/3gNmOAilwn8aH0wiVczPw0scLV+4C3gMLftYC2 F7YXslqJKpYGg== Message-ID: <11c6fd13-d2a2-4497-8417-d2176f1b5ecf@kernel.org> Date: Wed, 28 Oct 2026 11:06:46 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 01/15] mm/mempolicy: charge shared policy nodes To: Balbir Singh Cc: Andrew Morton , Gregory Price , Zi Yan , Joshua Hahn , Rakie Kim , Ying Huang , Johannes Weiner , Vladimir Davydov , Michal Hocko , Hugh Dickins , Baolin Wang , Lukas Czerner , Carlos Maiolino , Christian Brauner , Jan Kara , Daniel Verkamp , Jeff Xu , Muchun Song , Oscar Salvador , David Stevens , "Matthew Wilcox (Oracle)" , William Kucharski , Chris Li , Kairui Song , Nhat Pham , Miaohe Lin , Naoya Horiguchi , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chris Mason , stable@vger.kernel.org, Pedro Falcato , "Kiryl Shutsemau (Meta)" References: <20261028-fixes_shmem-v3-0-4ce3baf2db4b@kernel.org> <20261028-fixes_shmem-v3-1-4ce3baf2db4b@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E25E7A000D X-Stat-Signature: yjfeyrfw19yto1xw4zhb6g6byc8jw18c X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1793182017-584680 X-HE-Meta: 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 hei93fqp uhG+uUcE0faMFYg+sihs57wI+exwiftZ5k69mwYB2+I/2Bi94+FGWKuw43py1emt7Ft4q+6EdjiM1vA0lrqVAmunF+SGh1bHZi2NUEIZVtnEG6SYBsw56CVRGLspgcG8QDgmXKCe0BIkUc4GxGBTieopREvsPN1qyKYs/zej8s67wEDskYNvv29gr7nK7K4K26k1MEhSxxs5GrcjVpRqPmotKRTHCCkmmrBgQI8cpJV0Myjp7dMOownxB+es5L7osFnBpzEL9/hBGXnZvLkCQI35BZxlGI/bMHADDk35K8B+KKlvIKBqjNIvdRIJCkB/ts8gJtJEekynH+VVkcl1qLi8iZ7TFi6e75DxyzjcruBgYMWURtKCnBZ2DtZGEBXN9/CPBUgCzg07ZC68bJ+9oNckgQ6fBYPAxu34+tMbzYV25jFFeOmtaFHgKTkto+y6vBMSbJjWmCPUxYgfo23Hg1/XR0Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 10/28/26 11:02, Balbir Singh wrote: > On Wed, Oct 28, 2026 at 10:54:59AM +0100, David Hildenbrand (Arm) wrote: >> From: Chris Mason >> >> Any local user can bypass memory.max with mbind() on a tmpfs file, and >> allocate unbounded kernel memory. >> >> mbind() sets a NUMA memory policy for a range of a mapping. If the >> mapping is of a shmem and friends, the kernel also stores the policy on >> the inode, in a tree with one entry per range of the file. >> >> Each mbind() on a single page of a mapping can add one shared policy node >> (struct sp_node) and one struct mempolicy to that tree. They outlive the >> mapping and stay around until the inode is destroyed. The tree is not >> bounded by the file size, so the file can be empty. >> >> Memory that user space can allocate must be charged to a memory cgroup. A >> slab cache does that for all of its objects if it is created with >> SLAB_ACCOUNT. numa_policy_init() creates the slab caches for both >> structs without SLAB_ACCOUNT, so they are not charged to any cgroup. >> >> Reproduced with mbind() on single pages of an empty tmpfs file, from a >> cgroup with memory.max=8M: the global OOM killer killed tasks owned by >> root, and the machine panicked. >> >> Fix this by creating both caches with SLAB_ACCOUNT. This change implies >> that mbind() can now fail when running into memcg limits. Further, >> the policy_cache also serves task and VMA policies, so they are >> similarly accounted now. >> >> Note that per-file limits are not really helpful, as the user could >> simply use many files; having limits per user is tricky as well. >> >> Fix generated by an LLM and submitted by Chris Mason in private. >> >> Fixes: 5d097056c9a0 ("kmemcg: account certain kmem allocations to memcg") >> Cc: stable@vger.kernel.org >> Signed-off-by: Chris Mason >> Acked-by: Pedro Falcato >> Acked-by: Kiryl Shutsemau (Meta) >> Acked-by: Zi Yan >> Reviewed-by: Baolin Wang >> Tested-by: Gregory Price (Meta) >> [ david: smaller description tweaks ] >> Signed-off-by: David Hildenbrand (Arm) >> --- >> mm/mempolicy.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/mm/mempolicy.c b/mm/mempolicy.c >> index 0884c629670d..4da1cb8777f6 100644 >> --- a/mm/mempolicy.c >> +++ b/mm/mempolicy.c >> @@ -3372,11 +3372,11 @@ void __init numa_policy_init(void) >> >> policy_cache = kmem_cache_create("numa_policy", >> sizeof(struct mempolicy), >> - 0, SLAB_PANIC, NULL); >> + 0, SLAB_PANIC | SLAB_ACCOUNT, NULL); >> >> sn_cache = kmem_cache_create("shared_policy_node", >> sizeof(struct sp_node), >> - 0, SLAB_PANIC, NULL); >> + 0, SLAB_PANIC | SLAB_ACCOUNT, NULL); >> >> for_each_node(nid) { >> preferred_node_policy[nid] = (struct mempolicy) { >> > > You have many of them already, but anyway > > Reviewed-by: Balbir Singh I love it, thanks to all of you :) -- Cheers, David