linux-kernel - [PATCH] SLUB: Do not fallback to mininum order if __GFP

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Date:   Wed, 18 Apr 2018 09:45:39 -0500 (CDT)
From:   Christopher Lameter <cl@...ux.com>
To:     Vlastimil Babka <vbabka@...e.cz>
cc:     Mikulas Patocka <mpatocka@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Pekka Enberg <penberg@...nel.org>, linux-mm@...ck.org,
        dm-devel@...hat.com, David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] SLUB: Do not fallback to mininum order if __GFP_NORETRY is
 set

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@...ux.com>

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;
 		/*