[PATCH RFC 13/15] mm/slab: remove __GFP_NO_OBJ_EXT usage from alloc_slab_obj_exts()

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

__GFP_NO_OBJ_EXT has limited scope within the slab allocator itself and
gfp flags are a scarce resource, unlike slab's alloc_flags.

Introduce SLAB_ALLOC_NO_RECURSE alloc flag that has the same intent as
__GFP_NO_OBJ_EXT but a more generic name, meaning that a kmalloc()
family function should not recurse into another kmalloc*() for the
purposes of allocating auxiliary structures (obj_ext arrays or sheaves).

First, replace the __GFP_NO_OBJ_EXT for allocating obj_ext arrays in
alloc_slab_obj_exts(). Make use of the newly added kmalloc_flags()
function, where we can pass alloc_flags with SLAB_ALLOC_NO_RECURSE
added. This will also pass through SLAB_ALLOC_TRYLOCK so we don't need
to special case kmalloc_nolock() anymore.

Note that until now the kmalloc_nolock() ignored the incoming gfp flags
and hardcoded __GFP_ZERO | __GFP_NO_OBJ_EXT. But it's correct to pass on
the incoming gfp flags (only augmented with __GFP_ZERO), because if
alloc_flags contain SLAB_ALLOC_TRYLOCK, the incoming gfp flags have to
be also compatible with it.

Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
---
 mm/slab.h |  1 +
 mm/slub.c | 13 +++++--------
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/mm/slab.h b/mm/slab.h
index 13517abcad21..e5bd800d831e 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -20,6 +20,7 @@
 #define SLAB_ALLOC_DEFAULT	0x00
 #define SLAB_ALLOC_TRYLOCK	0x01
 #define SLAB_ALLOC_NEW_SLAB	0x02 /* a flag for alloc_slab_obj_exts() */
+#define SLAB_ALLOC_NO_RECURSE	0x04 /* prevent kmalloc() recursion */
 
 static inline bool alloc_flags_allow_spinning(const unsigned int alloc_flags)
 {
diff --git a/mm/slub.c b/mm/slub.c
index 86691eb14002..8a655636dee6 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2167,15 +2167,12 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
 
 	gfp &= ~OBJCGS_CLEAR_MASK;
 	/* Prevent recursive extension vector allocation */
-	gfp |= __GFP_NO_OBJ_EXT;
+	alloc_flags |= SLAB_ALLOC_NO_RECURSE;
 
 	sz = obj_exts_alloc_size(s, slab, gfp);
 
-	if (unlikely(!allow_spin))
-		vec = kmalloc_nolock(sz, __GFP_ZERO | __GFP_NO_OBJ_EXT,
-				     slab_nid(slab));
-	else
-		vec = kmalloc_node(sz, gfp | __GFP_ZERO, slab_nid(slab));
+	/* This will use kmalloc_nolock() if alloc_flags say so */
+	vec = kmalloc_flags(sz, gfp | __GFP_ZERO, alloc_flags, slab_nid(slab));
 
 	if (!vec) {
 		/*
@@ -2251,7 +2248,7 @@ static inline void free_slab_obj_exts(struct slab *slab, bool allow_spin)
 	}
 
 	/*
-	 * obj_exts was created with __GFP_NO_OBJ_EXT flag, therefore its
+	 * obj_exts was created with SLAB_ALLOC_NO_RECURSE flag, therefore its
 	 * corresponding extension will be NULL. alloc_tag_sub() will throw a
 	 * warning if slab has extensions but the extension of an object is
 	 * NULL, therefore replace NULL with CODETAG_EMPTY to indicate that
@@ -2374,7 +2371,7 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,
 	if (s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE))
 		return;
 
-	if (flags & __GFP_NO_OBJ_EXT)
+	if (alloc_flags & SLAB_ALLOC_NO_RECURSE)
 		return;
 
 	slab = virt_to_slab(object);

-- 
2.54.0