From 6a6b7b77cc0fdc13f50c66c219c8c05500a8dfce Mon Sep 17 00:00:00 2001 From: Muchun Song Date: Tue, 22 Mar 2022 14:40:53 -0700 Subject: mm: list_lru: transpose the array of per-node per-memcg lru lists Patch series "Optimize list lru memory consumption", v6. In our server, we found a suspected memory leak problem. The kmalloc-32 consumes more than 6GB of memory. Other kmem_caches consume less than 2GB memory. After our in-depth analysis, the memory consumption of kmalloc-32 slab cache is the cause of list_lru_one allocation. crash> p memcg_nr_cache_ids memcg_nr_cache_ids = $2 = 24574 memcg_nr_cache_ids is very large and memory consumption of each list_lru can be calculated with the following formula. num_numa_node * memcg_nr_cache_ids * 32 (kmalloc-32) There are 4 numa nodes in our system, so each list_lru consumes ~3MB. crash> list super_blocks | wc -l 952 Every mount will register 2 list lrus, one is for inode, another is for dentry. There are 952 super_blocks. So the total memory is 952 * 2 * 3 MB (~5.6GB). But now the number of memory cgroups is less than 500. So I guess more than 12286 memory cgroups have been created on this machine (I do not know why there are so many cgroups, it may be a user's bug or the user really want to do that). Because memcg_nr_cache_ids has not been reduced to a suitable value. It leads to waste a lot of memory. If we want to reduce memcg_nr_cache_ids, we have to *reboot* the server. This is not what we want. In order to reduce memcg_nr_cache_ids, I had posted a patchset [1] to do this. But this did not fundamentally solve the problem. We currently allocate scope for every memcg to be able to tracked on every superblock instantiated in the system, regardless of whether that superblock is even accessible to that memcg. These huge memcg counts come from container hosts where memcgs are confined to just a small subset of the total number of superblocks that instantiated at any given point in time. For these systems with huge container counts, list_lru does not need the capability of tracking every memcg on every superblock. What it comes down to is that the list_lru is only needed for a given memcg if that memcg is instatiating and freeing objects on a given list_lru. As Dave said, "Which makes me think we should be moving more towards 'add the memcg to the list_lru at the first insert' model rather than 'instantiate all at memcg init time just in case'." This patchset aims to optimize the list lru memory consumption from different aspects. I had done a easy test to show the optimization. I create 10k memory cgroups and mount 10k filesystems in the systems. We use free command to show how many memory does the systems comsumes after this operation (There are 2 numa nodes in the system). +-----------------------+------------------------+ | condition | memory consumption | +-----------------------+------------------------+ | without this patchset | 24464 MB | +-----------------------+------------------------+ | after patch 1 | 21957 MB | <--------+ +-----------------------+------------------------+ | | after patch 10 | 6895 MB | | +-----------------------+------------------------+ | | after patch 12 | 4367 MB | | +-----------------------+------------------------+ | | The more the number of nodes, the more obvious the effect---+ BTW, there was a recent discussion [2] on the same issue. [1] https://lore.kernel.org/all/20210428094949.43579-1-songmuchun@bytedance.com/ [2] https://lore.kernel.org/all/20210405054848.GA1077931@in.ibm.com/ This series not only optimizes the memory usage of list_lru but also simplifies the code. This patch (of 16): The current scheme of maintaining per-node per-memcg lru lists looks like: struct list_lru { struct list_lru_node *node; (for each node) struct list_lru_memcg *memcg_lrus; struct list_lru_one *lru[]; (for each memcg) } By effectively transposing the two-dimension array of list_lru_one's structures (per-node per-memcg => per-memcg per-node) it's possible to save some memory and simplify alloc/dealloc paths. The new scheme looks like: struct list_lru { struct list_lru_memcg *mlrus; struct list_lru_per_memcg *mlru[]; (for each memcg) struct list_lru_one node[0]; (for each node) } Memory savings are coming from not only 'struct rcu_head' but also some pointer arrays used to store the pointer to 'struct list_lru_one'. The array is per node and its size is 8 (a pointer) * num_memcgs. So the total size of the arrays is 8 * num_nodes * memcg_nr_cache_ids. After this patch, the size becomes 8 * memcg_nr_cache_ids. Link: https://lkml.kernel.org/r/20220228122126.37293-1-songmuchun@bytedance.com Link: https://lkml.kernel.org/r/20220228122126.37293-2-songmuchun@bytedance.com Signed-off-by: Muchun Song Acked-by: Johannes Weiner Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Vladimir Davydov Cc: Shakeel Butt Cc: Yang Shi Cc: Alex Shi Cc: Wei Yang Cc: Dave Chinner Cc: Trond Myklebust Cc: Anna Schumaker Cc: Jaegeuk Kim Cc: Chao Yu Cc: Kari Argillander Cc: Vlastimil Babka Cc: Qi Zheng Cc: Xiongchun Duan Cc: Fam Zheng Cc: Roman Gushchin Cc: Theodore Ts'o Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/list_lru.h | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-) (limited to 'include/linux') diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h index 1b5fceb565df..729a27b6ff53 100644 --- a/include/linux/list_lru.h +++ b/include/linux/list_lru.h @@ -31,10 +31,15 @@ struct list_lru_one { long nr_items; }; +struct list_lru_per_memcg { + /* array of per cgroup per node lists, indexed by node id */ + struct list_lru_one node[0]; +}; + struct list_lru_memcg { - struct rcu_head rcu; + struct rcu_head rcu; /* array of per cgroup lists, indexed by memcg_cache_id */ - struct list_lru_one *lru[]; + struct list_lru_per_memcg *mlru[]; }; struct list_lru_node { @@ -42,11 +47,7 @@ struct list_lru_node { spinlock_t lock; /* global list, used for the root cgroup in cgroup aware lrus */ struct list_lru_one lru; -#ifdef CONFIG_MEMCG_KMEM - /* for cgroup aware lrus points to per cgroup lists, otherwise NULL */ - struct list_lru_memcg __rcu *memcg_lrus; -#endif - long nr_items; + long nr_items; } ____cacheline_aligned_in_smp; struct list_lru { @@ -55,6 +56,8 @@ struct list_lru { struct list_head list; int shrinker_id; bool memcg_aware; + /* for cgroup aware lrus points to per cgroup lists, otherwise NULL */ + struct list_lru_memcg __rcu *mlrus; #endif }; -- cgit v1.2.3