CODEWITHSUNDEEP
memory-managementlinux-kernel
askb
askb

Reputation: 6768

unable to find new object create with kmem_cache_create() in /proc/slabinfo

I have written a simple kernel module which allocates objects using the slab layer. This module uses kernel API's (kmem_cache_{create,alloc,free}). The version of the kernel I am working on 3.15.4-200.

Though, my code works as expected with no issues, I am unable to see the new object/slab "my_cache" created using kmem_cache_create() when I grep /proc/slabinfo. The objects created are a simple list of objects, being inserted or removed from the list.

Note: My module works fine with no issues. I can view the slab creating under, /sys/kernel/slab/my_cache, but not in /proc/slabinfo or vmstat -m or slabtop 

mycache = kmem_cache_create("my_cache",
                 sizeof(struct mystruct),
                0, SLAB_HWCACHE_ALIGN, NULL);
if (mycache == NULL)
        return -ENOMEM;

`

$ sudo cat /sys/kernel/slab/my_cache/objects
49108 N0=49108
$ sudo cat /sys/kernel/slab/my_cache/object_size 
64
$ sudo cat /sys/kernel/slab/my_cache/order 
0
$ sudo cat /sys/kernel/slab/my_cache/aliases
12
$ sudo cat /sys/kernel/slab/my_cache/cache_dma 
0
$ sudo cat /sys/kernel/slab/my_cache/slab_size 
64
$ sudo cat /sys/kernel/slab/my_cache/trace 
0
$ sudo cat /sys/kernel/slab/my_cache/validate 
$ sudo cat /sys/kernel/slab/my_cache/total_objects 
49920 N0=49920

`

Upvotes: 4

Views: 2110

Answers (2)

KarimRaslan
KarimRaslan

Reputation: 333

kmem_cache_create usually tries to merge this cache with other caches. So for example if it found another cache for the same size with the same properties ( slab is going to be poisoned, etc ) it will just use this cache instead of creating a new cache.

If you really want to make sure that it'll definitely create a new cache for you ( = appear in slabinfo ), you can always pass a valid constructor to kmem_cache_create. Something like this:

static void mystruct_constructor(void *addr)
{
    memset(addr, 0, sizeof(struct mystruct));
}

mycache = kmem_cache_create("my_cache",
            sizeof(struct mystruct),
            0, 0, mystruct_constructor);

A constructor is usually called for every object allocation from this cache.

Upvotes: 9

askb
askb

Reputation: 6768

passing the additional flag SLAB_POISON solves the issue.

from link SLAB_POISON - Poison the slab with a known test pattern (a5a5a5a5) to catch references to uninitialised memory.

Upvotes: 4

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