Re: [patch 1/5] mm: add nofail variants of kmalloc kcalloc and kzalloc

Christoph Lameter
2010-08-25T21:35:04Z

On Wed, 25 Aug 2010, David Rientjes wrote:

> It all depends on what flags are passed to kmalloc(), slab nor slub
> enforce __GFP_NOFAIL behavior themselves. In slab, cache_grow() will
> return NULL depending on whether the page allocator returns NULL, and that
> would only happen for __GFP_NORETRY or
> cachep->gfp->gfporder >= PAGE_ALLOC_COSTLY_ORDER. In slub, the default
> order is tried with __GFP_NORETRY and if it returns NULL, the higher order
> alloc will fail under the same circumstances. So the nofail behavior for
> slab depends only on the flags passed from the caller.

If the higher order fails in slub then an order 0 alloc is attempted
without __GFP_NORETRY. In both cases the nofail behavior of the page
allocator determines the outcode.

True if the caller mixes in __GFP_NORETRY then you may still get NULL. But
that is an issue that can be resolved by the caller.