Re: [PATCH] Do not pass the SLAB flags as GFP in slob kmem_cache_create

Matt Mackall
2008-12-10T19:59:27Z

On Wed, 2008-12-10 at 22:34 +0300, Cyrill Gorcunov wrote:
> [Catalin Marinas - Wed, Dec 10, 2008 at 05:36:33PM +0000]
> | It looks like the kmem_cache_create() function in the slob allocator
> | passes the SLAB flags as GFP flags to the slob_alloc() function. The
> | patch changes this call to pass GFP_KERNEL as the other allocators seem
> | to do.
> |
> | Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> | Cc: Matt Mackall <mpm@selenic.com>
> | ---
> | mm/slob.c | 2 +-
> | 1 files changed, 1 insertions(+), 1 deletions(-)
> |
> | diff --git a/mm/slob.c b/mm/slob.c
> | index ff5a98d..dce9258 100644
> | --- a/mm/slob.c
> | +++ b/mm/slob.c
> | @@ -538,7 +538,7 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
> | struct kmem_cache *c;
> |
> | c = slob_alloc(sizeof(struct kmem_cache),
> | - flags, ARCH_KMALLOC_MINALIGN, -1);
> | + GFP_KERNEL, ARCH_KMALLOC_MINALIGN, -1);
> |
> | if (c) {
> | c->name = name;
> |
>
> Hi Catalin,
>
> this would make the following line in slob_alloc
>
> ...
> if (unlikely((gfp & __GFP_ZERO) && b))
> memset(b, 0, size);
> ...
>
> useless. Not sure if it will be good :)

I think that's fine. Notice that this is not the allocation of an
object, but the allocation of a cache descriptor. We save the flags
inside the descriptor so that when the user calls kmem_cache_alloc, we
can pass them along to slob_alloc, where GFP_ZERO can take effect.

So, if we're comfortable with the idea that we can only create caches in
'normal' contexts, then I think the patch is fine.

--
Mathematics is the supreme nostalgia of our time.