On Wed, 18 Apr 2018, Christopher Lameter wrote:
> Mikulas Patoka wants to ensure that no fallback to lower order happens. I
> think __GFP_NORETRY should work correctly in that case too and not fall
> back.
>
>
>
> Allocating at a smaller order is a retry operation and should not
> be attempted.
>
> If the caller does not want retries then respect that.
>
> GFP_NORETRY allows callers to ensure that only maximum order
> allocations are attempted.
>
> Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
>
> Index: linux/mm/slub.c
> ===================================================================
> --- linux.orig/mm/slub.c
> +++ linux/mm/slub.c
> @@ -1598,7 +1598,7 @@ static struct page *allocate_slab(struct
> alloc_gfp = (alloc_gfp | __GFP_NOMEMALLOC) & ~(__GFP_RECLAIM|__GFP_NOFAIL);
>
> page = alloc_slab_page(s, alloc_gfp, node, oo);
> - if (unlikely(!page)) {
> + if (unlikely(!page) && !(flags & __GFP_NORETRY)) {
> oo = s->min;
> alloc_gfp = flags;
> /*
No, this would hit NULL pointer dereference if page is NULL and
__GFP_NORETRY is set. You want this:
---
mm/slub.c | 2 ++
1 file changed, 2 insertions(+)
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c 2018-04-17 20:58:23.000000000 +0200
+++ linux-2.6/mm/slub.c 2018-04-18 17:04:01.000000000 +0200
@@ -1599,6 +1599,8 @@ static struct page *allocate_slab(struct
page = alloc_slab_page(s, alloc_gfp, node, oo);
if (unlikely(!page)) {
+ if (flags & __GFP_NORETRY)
+ goto out;
oo = s->min;
alloc_gfp = flags;
/*
