Messages in this thread | | | Date | Wed, 9 Jul 2008 13:06:45 +0300 | From | "Pekka Enberg" <> | Subject | Re: Kmem_cache handling in linux-2.6.2x kernel |
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Hi,
On Wed, Jul 9, 2008 at 8:06 AM, <KokHow.Teh@infineon.com> wrote: > I have a question about kmem_cache implemented in Linux-2.6.2x > kernel. I have an application that allocates and free 64KByte chunks of > memory (32-byte aligned) quite often. Therefore, I create a lookaside > cache for that purpose and use kmem_cache_alloc(), kmem_cache_free() to > allocate and free the caches. The application works very well in this > model. However, my concern here is if kmem_cache_free() does return the > cache to the system-wide pool so that it could be used by other > applications when need arises; when system is low in memory resources, > for instance. This is a question about the internal workings of the > memory management system of the Linux-2.6.2x kernel as to how efficient > it manages this lookasie caches. The concern is valid because if this > lookaside cache is not managed well, i.e, it is not returned to the > system-wide free memory pools to be used by other applications, this > will penalize the performace and throughput of the whole system due to > the dynamic behaviour of the utilization of system memory resources. For > example, other applications might be swapping in and out of the harddisk > and if the kmem_cache_free()'ed memory objects could be used by these > applications, it will help in this case to reduce the number of swaps > that happen, thereby freeing the CPU and/or DMA from doing the swapping > to do other critical tasks.
I'm not sure I understand the question. The pages allocated for a particular cache are given back to the page allocator whenever all objects of a slab are freed. In addition, SLUB does slab merging so the same cache can be transparently used by other kmem_cache_alloc() callers. So there really are no reservation guarantees for a cache in OOM conditions.
On Wed, Jul 9, 2008 at 8:06 AM, <KokHow.Teh@infineon.com> wrote: > On the other hand, if the caches are returned to the system-wide > free memory pool, what are the advantages of using kmem_cache_t compared > to the conventional kmalloc()/kfree()?
The main advantages for using kmem_cache_create() are that (1) you control the alignment and (2) you get tighter packing for the objects (less internal fragmentation).
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