Re: [PATCH v2 09/16] rcu/tree: Maintain separate array for vmalloc ptrs

Uladzislau Rezki
2020-06-18T18:23:42Z

On Thu, Jun 18, 2020 at 11:15:41AM -0700, Matthew Wilcox wrote:
> On Thu, Jun 18, 2020 at 07:56:23PM +0200, Uladzislau Rezki wrote:
> > If we mix pointers, then we can do free per pointer only. I mean in that
> > case we will not be able to use kfree_bulk() interface for freeing SLAB
> > memory and the code would converted to something like:
> >
> > <snip>
> > while (nr_objects_in_array > 0) {
> > if (is_vmalloc_addr(array[X]))
> > vfree(array[X]);
> > else
> > kfree(array[X]);
> > }
> > <snip>
>
> [PATCH] Add vfree_bulk interface
>
> This is a useful interface to have for the RCU kvfree code. There is
> scope for more performance gains later, but introducing the interface
> now allows us to simplify the RCU code today.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
>
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 48bb681e6c2a..dc2bbb61af61 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -119,6 +119,7 @@ void *__vmalloc_node(unsigned long size, unsigned long align, gfp_t gfp_mask,
>
> extern void vfree(const void *addr);
> extern void vfree_atomic(const void *addr);
> +extern void vfree_bulk(size_t count, void **addrs);
>
> extern void *vmap(struct page **pages, unsigned int count,
> unsigned long flags, pgprot_t prot);
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index abe37f09ac42..6042f9b4394a 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2366,6 +2366,22 @@ void vfree(const void *addr)
> }
> EXPORT_SYMBOL(vfree);
>
> +void vfree_bulk(size_t count, void **addrs)
> +{
> + unsigned int i;
> +
> + BUG_ON(in_nmi());
> + might_sleep_if(!in_interrupt());
> +
> + for (i = 0; i < count; i++) {
> + void *addr = addrs[i];
> + kmemleak_free(addr);
> + if (addr)
> + __vfree(addr);
> + }
> +}
> +EXPORT_SYMBOL(vfree_bulk);
> +
>
Can we just do addrs[i] all over the loop?

Also, we can just call vfree() instead that has all checking we
need: NMI, kmemleak, might_sleep.

Thanks!

--
Vlad Rezki