kmem_cache_zalloc

I'd really go for k(mem_)zalloc, but a kmem_cache_alloc leads people toward writing bad code. The purpose of the slab allocator is to allow caching readily constructed objects, a _zalloc destroys them on alloc.

I thought that the life span of an object is between
kmem_cache_alloc and kmem_cache_free. If you are expecting caching beyond this, you may not get correct data. kmem_cache allocator is supposed to quickly allocate fixed size structures avoiding the need for frequent splitting and coalescing in the allocator.

Am I missing something here ?

Quoted 7 lines · [email protected] said:

I thought that the life span of an object is between
kmem_cache_alloc and kmem_cache_free. If you are expecting caching beyond this, you may not get correct data. kmem_cache allocator is supposed to quickly allocate fixed size structures avoiding the need for frequent splitting and coalescing in the allocator.

Am I missing something here ?

Yes. Slab objects can be initialised once when a new page is added to the slab, and returned to the slab in reusable form so that you don't have the cost of complete initialisation on each allocation.

So if for example you have a semaphore in your slab object, instead of initialising it on each kmem_cache_alloc() you do it once when the new pages are added to the slab. Then you just make sure it's unlocked each time you free a slab object.