Re: [RFC 2/7] mm/vmalloc: Support non-blocking GFP flags in alloc_vmap_area()

Uladzislau Rezki
2025-07-08T12:34:36Z

On Mon, Jul 07, 2025 at 09:11:35AM +0200, Michal Hocko wrote:
> On Fri 04-07-25 17:25:32, Uladzislau Rezki wrote:
> [...]
> > @@ -2030,7 +2033,8 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
> > */
> > va = node_alloc(size, align, vstart, vend, &addr, &vn_id);
> > if (!va) {
> > - gfp_mask = gfp_mask & GFP_RECLAIM_MASK;
> > + if (allow_block)
> > + gfp_mask = gfp_mask & GFP_RECLAIM_MASK;
>
> I don't follow here and is this even correct?
>
Allow nested flags to follow a user request if there is a request
to not block. For example if we apply GFP_RECLAIM_MASK to GFP_ATOMIC
GFP_ATOMIC is converted to zero, thus to GFP_NOWAIT.

> >
> > va = kmem_cache_alloc_node(vmap_area_cachep, gfp_mask, node);
> > if (unlikely(!va))
> > @@ -2057,8 +2061,14 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
> > * If an allocation fails, the error value is
> > * returned. Therefore trigger the overflow path.
> > */
> > - if (IS_ERR_VALUE(addr))
> > + if (IS_ERR_VALUE(addr)) {
> > + if (!allow_block) {
> > + kmem_cache_free(vmap_area_cachep, va);
> > + return ERR_PTR(-ENOMEM);
>
> I would suggest to add a comment for this. Something like
>
> for blockable requests trigger the overflow paths because that
> relies on vmap_purge_lock mutex and blocking notifiers.
>
Thanks, i can do it easily. Also, this is an RFC i think it should
be split and improved. Maybe to move out some functionality into a
separate function.

--
Uladzislau Rezki