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b=F4nu0SdSgFBEzn6o6+oNrlQuLG135cNvyhQYIDgRsQUK+F7DrNz1Zcqd8jYSkU8DU 6vcL8dKo5ivufAP+wN24W/BtE5lfRnQ+2h4p7tg82jFaUcBvqTKaWvMwrPzyvLnhKH SzQ0ZZaF79lv4go65JrioUojE5ON6/+66a7vW77C88/a0dOC0S10tKls2pO6G5NZtv YP4fOMVHRmmYNbtDx7bH2owseWaURPy8ErZcC8K9x53u7oFccKeGmz2Lkzu3IcPLZg 6zEGLvF4mjK0KZ3BeaqJkqBRqDa9KkuGeYzaQNLk55JFWdKqjOiqSuGxytxppQyD3q 4wrUhvkoyBSUg== Message-ID: <94d89d84-c009-470e-a401-1ac75228cd92@kernel.org> Date: Fri, 13 Mar 2026 10:46:15 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: "Vlastimil Babka (SUSE)" Subject: Re: [PATCH 1/3] slab: decouple pointer to barn from kmem_cache_node Content-Language: en-US To: Harry Yoo Cc: Ming Lei , Hao Li , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260311-b4-slab-memoryless-barns-v1-0-70ab850be4ce@kernel.org> <20260311-b4-slab-memoryless-barns-v1-1-70ab850be4ce@kernel.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: B547518000B X-Stat-Signature: swdo8hrmdr4mqcyjasnnupcxqxmgjwr9 X-Rspam-User: X-HE-Tag: 1773395179-165705 X-HE-Meta: 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 LDVpI7ni isfhpaJ1FdIH8FlPQIoO2qdZ0ZcyW9yRI/tXbPr33+34SXzc80knHbXi7SRCTVCPyg4zFs1uAZoFwky8P69DKABbZ5vPwo0TGEItAVD5GUia1a8w+oDfU9XSmC8lspt/cH5J5WYERPLkLVo3i5kEQHft6kjkBMlhBcI16z/TKdlDKprumSLdvhucWl7/QyAQKGjp6wNZ7Svx9URy1wCFI6+NPUAtQKThKUfAa4r/8YgOuBxMphJ4guTzVfcGB3YLLcGoI74K1otGdv2UjJCzi50MCtIBGnmjD9QcWXDvNqEKxcbbfW2Je6WHTtMwDGoYLN6u8ez+KprB2naI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/13/26 10:27, Harry Yoo wrote: > On Wed, Mar 11, 2026 at 09:25:55AM +0100, Vlastimil Babka (SUSE) wrote: >> The pointer to barn currently exists in struct kmem_cache_node. That >> struct is instantiated for every NUMA node with memory, but we want to >> have a barn for every online node (including memoryless). >> >> Thus decouple the two structures. In struct kmem_cache we have an array >> for kmem_cache_node pointers that appears to be sized MAX_NUMNODES but >> the actual size calculation in kmem_cache_init() uses nr_node_ids. >> Therefore we can't just add another array of barn pointers. Instead >> change the array to newly introduced struct kmem_cache_per_node_ptrs >> holding both kmem_cache_node and barn pointer. >> >> Adjust barn accessor and allocation/initialization code accordingly. For >> now no functional change intended, barns are created 1:1 together with >> kmem_cache_nodes. >> >> Signed-off-by: Vlastimil Babka (SUSE) >> --- >> mm/slab.h | 7 +++- >> mm/slub.c | 128 +++++++++++++++++++++++++++++++++++--------------------------- >> 2 files changed, 78 insertions(+), 57 deletions(-) >> >> diff --git a/mm/slab.h b/mm/slab.h >> index e9ab292acd22..c735e6b4dddb 100644 >> --- a/mm/slab.h >> +++ b/mm/slab.h >> @@ -247,7 +252,7 @@ struct kmem_cache { >> struct kmem_cache_stats __percpu *cpu_stats; >> #endif >> >> - struct kmem_cache_node *node[MAX_NUMNODES]; >> + struct kmem_cache_per_node_ptrs per_node[MAX_NUMNODES]; >> }; > > We should probably turn this into a true flexible array at some point, > but that's out of scope for this patchset. Right. >> diff --git a/mm/slub.c b/mm/slub.c >> index 20cb4f3b636d..609a183f8533 100644 >> --- a/mm/slub.c >> +++ b/mm/slub.c >> @@ -436,26 +436,24 @@ struct kmem_cache_node { >> /* >> - * Get the barn of the current cpu's closest memory node. It may not exist on >> - * systems with memoryless nodes but without CONFIG_HAVE_MEMORYLESS_NODES >> + * Get the barn of the current cpu's memory node. It may be a memoryless node. >> */ >> static inline struct node_barn *get_barn(struct kmem_cache *s) >> { >> - struct kmem_cache_node *n = get_node(s, numa_mem_id()); >> - >> - if (!n) >> - return NULL; >> - >> - return n->barn; >> + return get_barn_node(s, numa_node_id()); >> } > > Previously, memoryless nodes on architectures w/ CONFIG_HAVE_MEMORYLESS_NODES > shared the barn of the nearest NUMA node with memory. > > But now memoryless nodes will have their own barns (after patch 2) > regardless of CONFIG_HAVE_MEMORYLESS_NODES, and that's intentional, right? Yeah it improves their caching capacity, but good point, will mention it in the changelog. > Otherwise LGTM! >