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.
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