mm/slab: pass __GFP_NOWARN to refill_sheaf() if fallback is available

When refill_sheaf() is called, failing to refill the sheaf doesn't
necessarily mean the allocation will fail because a fallback path
might be available and serve the allocation request.

Suppress spurious warnings by passing __GFP_NOWARN along with
__GFP_NOMEMALLOC whenever a fallback path is available.

When the caller is alloc_full_sheaf() or __pcs_replace_empty_main(),
the kernel always falls back to the slowpath (__slab_alloc_node()).
For __prefill_sheaf_pfmemalloc(), the fallback path is available
only when gfp_pfmemalloc_allowed() returns true.

Reported-and-tested-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Closes: https://lore.kernel.org/linux-mm/aZt2-oS9lkmwT7Ch@debian.local
Fixes: 1ce20c28eafd ("slab: handle pfmemalloc slabs properly with sheaves")
Link: https://lore.kernel.org/linux-mm/aZwSreGj9-HHdD-j@hyeyoo
Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
Link: https://patch.msgid.link/20260223133322.16705-1-harry.yoo@oracle.com
Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

diff --git a/mm/slub.c b/mm/slub.c
index 862642c165eddd36d22b941344250baf3b820823..4ce24d9ee7e4e79ff86e562521cd4f55f8cdcfb0 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2822,7 +2822,7 @@ static struct slab_sheaf *alloc_full_sheaf(struct kmem_cache *s, gfp_t gfp)
        if (!sheaf)
                return NULL;
 
-       if (refill_sheaf(s, sheaf, gfp | __GFP_NOMEMALLOC)) {
+       if (refill_sheaf(s, sheaf, gfp | __GFP_NOMEMALLOC | __GFP_NOWARN)) {
                free_empty_sheaf(s, sheaf);
                return NULL;
        }
@@ -4575,7 +4575,7 @@ __pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs,
                return NULL;
 
        if (empty) {
-               if (!refill_sheaf(s, empty, gfp | __GFP_NOMEMALLOC)) {
+               if (!refill_sheaf(s, empty, gfp | __GFP_NOMEMALLOC | __GFP_NOWARN)) {
                        full = empty;
                } else {
                        /*
@@ -4890,9 +4890,14 @@ EXPORT_SYMBOL(kmem_cache_alloc_node_noprof);
 static int __prefill_sheaf_pfmemalloc(struct kmem_cache *s,
                                      struct slab_sheaf *sheaf, gfp_t gfp)
 {
-       int ret = 0;
+       gfp_t gfp_nomemalloc;
+       int ret;
+
+       gfp_nomemalloc = gfp | __GFP_NOMEMALLOC;
+       if (gfp_pfmemalloc_allowed(gfp))
+               gfp_nomemalloc |= __GFP_NOWARN;
 
-       ret = refill_sheaf(s, sheaf, gfp | __GFP_NOMEMALLOC);
+       ret = refill_sheaf(s, sheaf, gfp_nomemalloc);
 
        if (likely(!ret || !gfp_pfmemalloc_allowed(gfp)))
                return ret;