[patch v2 2/5] mm: add nofail variant of kmem_cache_zalloc

[David Rientjes]

Add kmem_cache_zalloc_nofail().  This function is equivalent to
kmem_cache_zalloc(), except that it will never return NULL and instead
loop forever trying to allocate memory.

If the first allocation attempt fails because the page allocator doesn't 
implicitly loop, a warning will be emitted, including a call trace.
Subsequent failures will suppress this warning.

This was added as a helper function for documentation and auditability.
No future callers should be added.

Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
 fs/gfs2/meta_io.c    |    2 +-
 include/linux/slab.h |   17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletions(-)

diff --git a/fs/gfs2/meta_io.c b/fs/gfs2/meta_io.c
--- a/fs/gfs2/meta_io.c
+++ b/fs/gfs2/meta_io.c
@@ -289,7 +289,7 @@ void gfs2_attach_bufdata(struct gfs2_glock *gl, struct buffer_head *bh,
 		return;
 	}
 
-	bd = kmem_cache_zalloc(gfs2_bufdata_cachep, GFP_NOFS | __GFP_NOFAIL);
+	bd = kmem_cache_zalloc_nofail(gfs2_bufdata_cachep, GFP_NOFS);
 	bd->bd_bh = bh;
 	bd->bd_gl = gl;
 
diff --git a/include/linux/slab.h b/include/linux/slab.h
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -313,6 +313,23 @@ static inline void *kmem_cache_zalloc(struct kmem_cache *k, gfp_t flags)
 	return kmem_cache_alloc(k, flags | __GFP_ZERO);
 }
 
+/*
+ * NOTE: no new callers of this function should be implemented!
+ * All memory allocations should be failable whenever possible.
+ */
+static inline void *kmem_cache_zalloc_nofail(struct kmem_cache *k, gfp_t flags)
+{
+	void *ret;
+
+	for (;;) {
+		ret = kmem_cache_zalloc(k, flags);
+		if (ret)
+			return ret;
+		WARN_ON_ONCE(get_order(kmem_cache_size(k)) >
+						PAGE_ALLOC_COSTLY_ORDER);
+	}
+}
+
 /**
  * kzalloc - allocate memory. The memory is set to zero.
  * @size: how many bytes of memory are required.
--
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