Re: [RFC PATCH 1/2] slab: implement bulk alloc in SLAB allocator

[Christoph Lameter <cl@linux.com>]

On Thu, 3 Dec 2015, Jesper Dangaard Brouer wrote:

> +	size_t i;
> +
> +	flags &= gfp_allowed_mask;
> +	lockdep_trace_alloc(flags);
> +
> +	if (slab_should_failslab(s, flags))
> +		return 0;

Ok here is an overlap with slub;'s pre_alloc_hook() and that stuff is
really not allocator specific. Could make it generic and move the hook
calls into slab_common.c/slab.h? That also gives you the opportunity to
get the array option in there.

> +	s = memcg_kmem_get_cache(s, flags);
> +
> +	cache_alloc_debugcheck_before(s, flags);
> +
> +	local_irq_disable();
> +	for (i = 0; i < size; i++) {
> +		void *objp = __do_cache_alloc(s, flags);
> +
> +		// this call could be done outside IRQ disabled section
> +		objp = cache_alloc_debugcheck_after(s, flags, objp, _RET_IP_);
> +
> +		if (unlikely(!objp))
> +			goto error;
> +
> +		prefetchw(objp);

Is the prefetch really useful here? Only if these objects are immediately
used I would think.

> +		p[i] = objp;
> +	}
> +	local_irq_enable();
> +
> +	/* Kmemleak and kmemcheck outside IRQ disabled section */
> +	for (i = 0; i < size; i++) {
> +		void *x = p[i];
> +
> +		kmemleak_alloc_recursive(x, s->object_size, 1, s->flags, flags);
> +		kmemcheck_slab_alloc(s, flags, x, s->object_size);
> +	}
> +
> +	/* Clear memory outside IRQ disabled section */
> +	if (unlikely(flags & __GFP_ZERO))
> +		for (i = 0; i < size; i++)
> +			memset(p[i], 0, s->object_size);

Maybe make this one loop instead of two?


> +// FIXME: Trace call missing... should we create a bulk variant?
> +/*  Like:
> +	trace_kmem_cache_alloc(_RET_IP_, ret, s->object_size, s->size, flags);
> +*/

That trace call could be created when you do the genericization of the
hooks() which also involve debugging stuff.

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