Re: [PATCH v4 1/4] mm/slub: enable debugging memory wasting of kmalloc

[Feng Tang <feng.tang@intel.com>]

On Mon, Sep 05, 2022 at 03:33:14PM +0800, Vlastimil Babka wrote:
> On 9/5/22 09:06, Feng Tang wrote:
> > On Mon, Sep 05, 2022 at 02:29:51PM +0800, Vlastimil Babka wrote:
> >> 
> >> How about get_partial() instantiates an on-stack structure that contains
> >> gfpflags, ret_slab, orig_size and passes pointer to that to all the nested
> >> functions.
> >> 
> >> Would be similar to "struct alloc_context" in page allocation.
> >> Something like "struct partial_context pc"?
> > 
> > Yep! This would make the parameters passing much tidier. Will try
> > this way. 
> > 
> > More aggressively is to also embed the 'kmem_cache' parameter into
> > it, but this may make the code look ambiguous.
> 
> That one is used a lot everywhere, so it would be tedious to dereference it
> from a struct, and also might be a bit better code if it's in a register.

Got it. Following is the incremental patch for 1/4, which uses the
'partial_context' to pass parameters. And actually the 4/4 patch will
benefit more from this refactoring, as the object initialization doesn't
need to be separated and has race issue.

Thanks,
Feng

---
diff --git a/mm/slub.c b/mm/slub.c
index 82e7bd3a3966..7497fb6ca8e2 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -194,6 +194,12 @@ DEFINE_STATIC_KEY_FALSE(slub_debug_enabled);
 #endif
 #endif		/* CONFIG_SLUB_DEBUG */
 
+struct partial_context {
+	struct slab **slab;
+	gfp_t flags;
+	int orig_size;
+};
+
 static inline bool kmem_cache_debug(struct kmem_cache *s)
 {
 	return kmem_cache_debug_flags(s, SLAB_DEBUG_FLAGS);
@@ -1333,7 +1339,7 @@ static inline int alloc_consistency_checks(struct kmem_cache *s,
 }
 
 static noinline int alloc_debug_processing(struct kmem_cache *s,
-					struct slab *slab, void *object)
+			struct slab *slab, void *object, int orig_size)
 {
 	if (s->flags & SLAB_CONSISTENCY_CHECKS) {
 		if (!alloc_consistency_checks(s, slab, object))
@@ -1342,6 +1348,7 @@ static noinline int alloc_debug_processing(struct kmem_cache *s,
 
 	/* Success. Perform special debug activities for allocs */
 	trace(s, slab, object, 1);
+	set_orig_size(s, object, orig_size);
 	init_object(s, object, SLUB_RED_ACTIVE);
 	return 1;
 
@@ -1610,7 +1617,7 @@ static inline
 void setup_slab_debug(struct kmem_cache *s, struct slab *slab, void *addr) {}
 
 static inline int alloc_debug_processing(struct kmem_cache *s,
-	struct slab *slab, void *object) { return 0; }
+	struct slab *slab, void *object, int orig_size) { return 0; }
 
 static inline void set_orig_size(struct kmem_cache *s,
 	void *object, unsigned int orig_size) {}
@@ -2042,7 +2049,7 @@ static inline void remove_partial(struct kmem_cache_node *n,
  * it to full list if it was the last free object.
  */
 static void *alloc_single_from_partial(struct kmem_cache *s,
-		struct kmem_cache_node *n, struct slab *slab)
+		struct kmem_cache_node *n, struct slab *slab, int orig_size)
 {
 	void *object;
 
@@ -2052,7 +2059,7 @@ static void *alloc_single_from_partial(struct kmem_cache *s,
 	slab->freelist = get_freepointer(s, object);
 	slab->inuse++;
 
-	if (!alloc_debug_processing(s, slab, object)) {
+	if (!alloc_debug_processing(s, slab, object, orig_size)) {
 		remove_partial(n, slab);
 		return NULL;
 	}
@@ -2071,7 +2078,7 @@ static void *alloc_single_from_partial(struct kmem_cache *s,
  * and put the slab to the partial (or full) list.
  */
 static void *alloc_single_from_new_slab(struct kmem_cache *s,
-					struct slab *slab)
+					struct slab *slab, int orig_size)
 {
 	int nid = slab_nid(slab);
 	struct kmem_cache_node *n = get_node(s, nid);
@@ -2083,7 +2090,7 @@ static void *alloc_single_from_new_slab(struct kmem_cache *s,
 	slab->freelist = get_freepointer(s, object);
 	slab->inuse = 1;
 
-	if (!alloc_debug_processing(s, slab, object))
+	if (!alloc_debug_processing(s, slab, object, orig_size))
 		/*
 		 * It's not really expected that this would fail on a
 		 * freshly allocated slab, but a concurrent memory
@@ -2161,7 +2168,7 @@ static inline bool pfmemalloc_match(struct slab *slab, gfp_t gfpflags);
  * Try to allocate a partial slab from a specific node.
  */
 static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
-			      struct slab **ret_slab, gfp_t gfpflags)
+			      struct partial_context *pc)
 {
 	struct slab *slab, *slab2;
 	void *object = NULL;
@@ -2181,11 +2188,11 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
 	list_for_each_entry_safe(slab, slab2, &n->partial, slab_list) {
 		void *t;
 
-		if (!pfmemalloc_match(slab, gfpflags))
+		if (!pfmemalloc_match(slab, pc->flags))
 			continue;
 
 		if (kmem_cache_debug(s)) {
-			object = alloc_single_from_partial(s, n, slab);
+			object = alloc_single_from_partial(s, n, slab, pc->orig_size);
 			if (object)
 				break;
 			continue;
@@ -2196,7 +2203,7 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
 			break;
 
 		if (!object) {
-			*ret_slab = slab;
+			*pc->slab = slab;
 			stat(s, ALLOC_FROM_PARTIAL);
 			object = t;
 		} else {
@@ -2220,14 +2227,13 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
 /*
  * Get a slab from somewhere. Search in increasing NUMA distances.
  */
-static void *get_any_partial(struct kmem_cache *s, gfp_t flags,
-			     struct slab **ret_slab)
+static void *get_any_partial(struct kmem_cache *s, struct partial_context *pc)
 {
 #ifdef CONFIG_NUMA
 	struct zonelist *zonelist;
 	struct zoneref *z;
 	struct zone *zone;
-	enum zone_type highest_zoneidx = gfp_zone(flags);
+	enum zone_type highest_zoneidx = gfp_zone(pc->flags);
 	void *object;
 	unsigned int cpuset_mems_cookie;
 
@@ -2255,15 +2261,15 @@ static void *get_any_partial(struct kmem_cache *s, gfp_t flags,
 
 	do {
 		cpuset_mems_cookie = read_mems_allowed_begin();
-		zonelist = node_zonelist(mempolicy_slab_node(), flags);
+		zonelist = node_zonelist(mempolicy_slab_node(), pc->flags);
 		for_each_zone_zonelist(zone, z, zonelist, highest_zoneidx) {
 			struct kmem_cache_node *n;
 
 			n = get_node(s, zone_to_nid(zone));
 
-			if (n && cpuset_zone_allowed(zone, flags) &&
+			if (n && cpuset_zone_allowed(zone, pc->flags) &&
 					n->nr_partial > s->min_partial) {
-				object = get_partial_node(s, n, ret_slab, flags);
+				object = get_partial_node(s, n, pc);
 				if (object) {
 					/*
 					 * Don't check read_mems_allowed_retry()
@@ -2284,8 +2290,7 @@ static void *get_any_partial(struct kmem_cache *s, gfp_t flags,
 /*
  * Get a partial slab, lock it and return it.
  */
-static void *get_partial(struct kmem_cache *s, gfp_t flags, int node,
-			 struct slab **ret_slab)
+static void *get_partial(struct kmem_cache *s, int node, struct partial_context *pc)
 {
 	void *object;
 	int searchnode = node;
@@ -2293,11 +2298,11 @@ static void *get_partial(struct kmem_cache *s, gfp_t flags, int node,
 	if (node == NUMA_NO_NODE)
 		searchnode = numa_mem_id();
 
-	object = get_partial_node(s, get_node(s, searchnode), ret_slab, flags);
+	object = get_partial_node(s, get_node(s, searchnode), pc);
 	if (object || node != NUMA_NO_NODE)
 		return object;
 
-	return get_any_partial(s, flags, ret_slab);
+	return get_any_partial(s, pc);
 }
 
 #ifdef CONFIG_PREEMPTION
@@ -3022,6 +3027,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	void *freelist;
 	struct slab *slab;
 	unsigned long flags;
+	struct partial_context pc;
 
 	stat(s, ALLOC_SLOWPATH);
 
@@ -3135,7 +3141,10 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 
 new_objects:
 
-	freelist = get_partial(s, gfpflags, node, &slab);
+	pc.flags = gfpflags;
+	pc.slab = &slab;
+	pc.orig_size = orig_size;
+	freelist = get_partial(s, node, &pc);
 	if (freelist)
 		goto check_new_slab;
 
@@ -3151,14 +3160,13 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	stat(s, ALLOC_SLAB);
 
 	if (kmem_cache_debug(s)) {
-		freelist = alloc_single_from_new_slab(s, slab);
+		freelist = alloc_single_from_new_slab(s, slab, orig_size);
 
 		if (unlikely(!freelist))
 			goto new_objects;
 
 		if (s->flags & SLAB_STORE_USER)
 			set_track(s, freelist, TRACK_ALLOC, addr);
-		set_orig_size(s, freelist, orig_size);
 
 		return freelist;
 	}
@@ -3184,7 +3192,6 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 		 */
 		if (s->flags & SLAB_STORE_USER)
 			set_track(s, freelist, TRACK_ALLOC, addr);
-		set_orig_size(s, freelist, orig_size);
 
 		return freelist;
 	}