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

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.