Re: Slab infrastructure for bulk object allocation and freeing V2

From: Andrew Morton
Date: Thu Apr 02 2015 - 16:42:45 EST

On Thu, 2 Apr 2015 09:25:37 -0500 (CDT) Christoph Lameter <cl@xxxxxxxxx> wrote:

> > What's the reason for returning a partial result when ENOMEM? Some
> > callers will throw away the partial result and simply fail out. If a
> > caller attempts to go ahead and use the partial result then great, but
> > you can bet that nobody will actually runtime test this situation, so
> > the interface is an invitation for us to release partially-tested code
> > into the wild.
> Just rely on the fact that small allocations never fail? The caller get
> all the requested objects if the function returns?

I'd suggest the latter: either the callee successfully allocates all
the requested objects or it fails.

> > Instead of the above, did you consider doing
> >
> > int __weak kmem_cache_alloc_array(struct kmem_cache *s, gfp_t flags, size_t nr,
> >
> > ?
> >
> > This way we save a level of function call and all that wrapper code in
> > the allocators simply disappears.
> I think we will need the auxiliary function in the common code later
> because that allows the allocations to only do the allocations that
> can be optimized and for the rest just fall back to the generic
> implementations. There may be situations in which the optimizations wont
> work. For SLUB this may be the case f.e. if debug options are enabled.

hm, OK. The per-allocator wrappers could be made static inline in .h
if that makes sense.

With the current code, gcc should be able to convert the call into a



pushq %rbp #
movq %rsp, %rbp #,
call __kmem_cache_free_array #

stupid gcc.
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