On Thu, 5 Sep 2024 15:47:23 +0900 Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> wrote:
> Each zsmalloc pool maintains several named kmem-caches for
> zs_handle-s and zspage-s. On a system with multiple zsmalloc
> pools and CONFIG_DEBUG_VM this triggers kmem_cache_sanity_check():
>
> kmem_cache of name 'zspage' already exists
> WARNING: at mm/slab_common.c:108 do_kmem_cache_create_usercopy+0xb5/0x310
> ...
>
> kmem_cache of name 'zs_handle' already exists
> WARNING: at mm/slab_common.c:108 do_kmem_cache_create_usercopy+0xb5/0x310
> ...
This is old code. Did something recently change to trigger this warning?
> We provide zram device name when init its zsmalloc pool, so we can
> use that same name for zsmalloc caches and, hence, create unique
> names that can easily be linked to zram device that has created
> them.
>
> So instead of having this
>
> cat /proc/slabinfo
> slabinfo - version: 2.1
> zspage 46 46 ...
> zs_handle 128 128 ...
> zspage 34270 34270 ...
> zs_handle 34816 34816 ...
> zspage 0 0 ...
> zs_handle 0 0 ...
>
> We now have this
>
> cat /proc/slabinfo
> slabinfo - version: 2.1
> zspage-zram2 46 46 ...
> zs_handle-zram2 128 128 ...
> zspage-zram0 34270 34270 ...
> zs_handle-zram0 34816 34816 ...
> zspage-zram1 0 0 ...
> zs_handle-zram1 0 0 ...
>
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -293,13 +293,17 @@ static void SetZsPageMovable(struct zs_pool *pool, struct zspage *zspage) {}
>
> static int create_cache(struct zs_pool *pool)
> {
> - pool->handle_cachep = kmem_cache_create("zs_handle", ZS_HANDLE_SIZE,
> - 0, 0, NULL);
> + char name[32];
> +
> + snprintf(name, sizeof(name), "zs_handle-%s", pool->name);
Always scary seeing code making such assumptions about it arguments in
this fashion. Can we use kasprintf() and sleep well at night?
> + pool->handle_cachep = kmem_cache_create(name, ZS_HANDLE_SIZE,
> + 0, 0, NULL);
> if (!pool->handle_cachep)
> return 1;
>
> - pool->zspage_cachep = kmem_cache_create("zspage", sizeof(struct zspage),
> - 0, 0, NULL);
> + snprintf(name, sizeof(name), "zspage-%s", pool->name);
> + pool->zspage_cachep = kmem_cache_create(name, sizeof(struct zspage),
> + 0, 0, NULL);
> if (!pool->zspage_cachep) {
> kmem_cache_destroy(pool->handle_cachep);
> pool->handle_cachep = NULL;
I guess we want to backport this into earlier kernels? If so, what
would be a suitable Fixes:?
