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From:   Oscar Salvador <osalvador@suse.de>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Michal Hocko <mhocko@suse.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Eric Dumazet <edumazet@google.com>,
        Waiman Long <longman@redhat.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Marco Elver <elver@google.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Alexander Potapenko <glider@google.com>,
        Oscar Salvador <osalvador@suse.de>
Subject: [PATCH v2 1/3] lib/stackdepot: Add a refcount field in stack_record
Date:   Mon,  5 Sep 2022 05:10:10 +0200
Message-Id: <20220905031012.4450-2-osalvador@suse.de>
In-Reply-To: <20220905031012.4450-1-osalvador@suse.de>
References: <20220905031012.4450-1-osalvador@suse.de>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
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We want to filter out page_owner output and print only those
stacks that have been repeated beyond a certain threshold.
This gives us the chance to get rid of a lot of noise.
In order to do that, we need to keep track of how many repeated stacks
(for allocation) do we have, so we add a new refcount_t field
in the stack_record struct.

Note that this might increase the size of the struct for some
architectures.
E.g: x86_64 is not affected due to alignment, but x86 32bits might.

The alternative would be to have some kind of struct like this:

struct track_stacks {
	struct stack_record *stack;
	struct track_stacks *next;
	refcount_t stack_count;

But ithat would imply to perform more allocations and glue everything
together, which would make the code more complex, so I think that
going with a new field in the struct stack_record is good enough.

Note that on __set_page_owner_handle(), page_owner->handle is set,
and on __reset_page_owner(), page_owner->free_handle is set.

We are interested in page_owner->handle, so when __set_page_owner()
gets called, we derive the stack_record struct from page_owner->handle,
and we increment its refcount_t field; and when __reset_page_owner()
gets called, we derive its stack_record from page_owner->handle()
and we decrement its refcount_t field.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
 include/linux/stackdepot.h | 13 ++++++-
 lib/stackdepot.c           | 79 +++++++++++++++++++++++++++++++-------
 mm/kasan/common.c          |  3 +-
 mm/page_owner.c            | 14 +++++--
 4 files changed, 89 insertions(+), 20 deletions(-)

diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
index bc2797955de9..4e3a88f135ee 100644
--- a/include/linux/stackdepot.h
+++ b/include/linux/stackdepot.h
@@ -15,9 +15,16 @@
 
 typedef u32 depot_stack_handle_t;
 
+enum stack_depot_action {
+	STACK_DEPOT_ACTION_NONE,
+	STACK_DEPOT_ACTION_COUNT,
+};
+
 depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 					unsigned int nr_entries,
-					gfp_t gfp_flags, bool can_alloc);
+					gfp_t gfp_flags, bool can_alloc,
+					enum stack_depot_action action);
+void stack_depot_dec_count(depot_stack_handle_t handle);
 
 /*
  * Every user of stack depot has to call stack_depot_init() during its own init
@@ -55,6 +62,10 @@ static inline int stack_depot_early_init(void)	{ return 0; }
 
 depot_stack_handle_t stack_depot_save(unsigned long *entries,
 				      unsigned int nr_entries, gfp_t gfp_flags);
+depot_stack_handle_t stack_depot_save_action(unsigned long *entries,
+					     unsigned int nr_entries,
+					     gfp_t gfp_flags,
+					     enum stack_depot_action action);
 
 unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 			       unsigned long **entries);
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index e73fda23388d..a806ef58a385 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -64,6 +64,7 @@ struct stack_record {
 	u32 hash;			/* Hash in the hastable */
 	u32 size;			/* Number of frames in the stack */
 	union handle_parts handle;
+	refcount_t count;		/* Number of the same repeated stacks */
 	unsigned long entries[];	/* Variable-sized array of entries. */
 };
 
@@ -140,6 +141,7 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
 	stack->handle.slabindex = depot_index;
 	stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN;
 	stack->handle.valid = 1;
+	refcount_set(&stack->count, 1);
 	memcpy(stack->entries, entries, flex_array_size(stack, entries, size));
 	depot_offset += required_size;
 
@@ -341,6 +343,29 @@ void stack_depot_print(depot_stack_handle_t stack)
 }
 EXPORT_SYMBOL_GPL(stack_depot_print);
 
+static struct stack_record *stack_depot_getstack(depot_stack_handle_t handle)
+{
+	union handle_parts parts = { .handle = handle };
+	void *slab;
+	size_t offset = parts.offset << STACK_ALLOC_ALIGN;
+	struct stack_record *stack;
+
+	if(!handle)
+		return NULL;
+
+	if (parts.slabindex > depot_index) {
+		WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
+		     parts.slabindex, depot_index, handle);
+		return NULL;
+	}
+	slab = stack_slabs[parts.slabindex];
+	if (!slab)
+		return NULL;
+
+	stack = slab + offset;
+	return stack;
+}
+
 /**
  * stack_depot_fetch - Fetch stack entries from a depot
  *
@@ -353,30 +378,42 @@ EXPORT_SYMBOL_GPL(stack_depot_print);
 unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 			       unsigned long **entries)
 {
-	union handle_parts parts = { .handle = handle };
-	void *slab;
-	size_t offset = parts.offset << STACK_ALLOC_ALIGN;
 	struct stack_record *stack;
 
 	*entries = NULL;
 	if (!handle)
 		return 0;
 
-	if (parts.slabindex > depot_index) {
-		WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
-			parts.slabindex, depot_index, handle);
-		return 0;
-	}
-	slab = stack_slabs[parts.slabindex];
-	if (!slab)
+	stack = stack_depot_getstack(handle);
+	if (!stack)
 		return 0;
-	stack = slab + offset;
 
 	*entries = stack->entries;
 	return stack->size;
 }
 EXPORT_SYMBOL_GPL(stack_depot_fetch);
 
+static void stack_depot_inc_count(struct stack_record *stack)
+{
+	refcount_inc(&stack->count);
+}
+
+void stack_depot_dec_count(depot_stack_handle_t handle)
+{
+	struct stack_record *stack = NULL;
+
+	stack = stack_depot_getstack(handle);
+	if (stack) {
+		/*
+		 * page_owner creates some stacks via create_dummy_stack().
+		 * We are not interested in those, so make sure we only decrement
+		 * "valid" stacks.
+		 */
+		if (refcount_read(&stack->count) > 1)
+			refcount_dec(&stack->count);
+	}
+}
+
 /**
  * __stack_depot_save - Save a stack trace from an array
  *
@@ -402,7 +439,8 @@ EXPORT_SYMBOL_GPL(stack_depot_fetch);
  */
 depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 					unsigned int nr_entries,
-					gfp_t alloc_flags, bool can_alloc)
+					gfp_t alloc_flags, bool can_alloc,
+					enum stack_depot_action action)
 {
 	struct stack_record *found = NULL, **bucket;
 	depot_stack_handle_t retval = 0;
@@ -488,8 +526,11 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 		/* Nobody used this memory, ok to free it. */
 		free_pages((unsigned long)prealloc, STACK_ALLOC_ORDER);
 	}
-	if (found)
+	if (found) {
 		retval = found->handle.handle;
+		if (action == STACK_DEPOT_ACTION_COUNT)
+			stack_depot_inc_count(found);
+	}
 fast_exit:
 	return retval;
 }
@@ -511,6 +552,16 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
 				      unsigned int nr_entries,
 				      gfp_t alloc_flags)
 {
-	return __stack_depot_save(entries, nr_entries, alloc_flags, true);
+	return __stack_depot_save(entries, nr_entries, alloc_flags, true,
+				  STACK_DEPOT_ACTION_NONE);
 }
 EXPORT_SYMBOL_GPL(stack_depot_save);
+
+depot_stack_handle_t stack_depot_save_action(unsigned long *entries,
+					     unsigned int nr_entries,
+					     gfp_t alloc_flags,
+					     enum stack_depot_action action)
+{
+	return __stack_depot_save(entries, nr_entries, alloc_flags, true, action);
+}
+EXPORT_SYMBOL_GPL(stack_depot_save_action);
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 69f583855c8b..8077c6e70815 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -36,7 +36,8 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc)
 	unsigned int nr_entries;
 
 	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
-	return __stack_depot_save(entries, nr_entries, flags, can_alloc);
+	return __stack_depot_save(entries, nr_entries, flags, can_alloc,
+				  STACK_DEPOT_ACTION_NONE);
 }
 
 void kasan_set_track(struct kasan_track *track, gfp_t flags)
diff --git a/mm/page_owner.c b/mm/page_owner.c
index e4c6f3f1695b..8730f377fa91 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -106,7 +106,8 @@ static inline struct page_owner *get_page_owner(struct page_ext *page_ext)
 	return (void *)page_ext + page_owner_ops.offset;
 }
 
-static noinline depot_stack_handle_t save_stack(gfp_t flags)
+static noinline depot_stack_handle_t save_stack(gfp_t flags,
+						enum stack_depot_action action)
 {
 	unsigned long entries[PAGE_OWNER_STACK_DEPTH];
 	depot_stack_handle_t handle;
@@ -125,7 +126,7 @@ static noinline depot_stack_handle_t save_stack(gfp_t flags)
 	current->in_page_owner = 1;
 
 	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
-	handle = stack_depot_save(entries, nr_entries, flags);
+	handle = stack_depot_save_action(entries, nr_entries, flags, action);
 	if (!handle)
 		handle = failure_handle;
 
@@ -138,6 +139,7 @@ void __reset_page_owner(struct page *page, unsigned short order)
 	int i;
 	struct page_ext *page_ext;
 	depot_stack_handle_t handle;
+	depot_stack_handle_t alloc_handle;
 	struct page_owner *page_owner;
 	u64 free_ts_nsec = local_clock();
 
@@ -145,7 +147,10 @@ void __reset_page_owner(struct page *page, unsigned short order)
 	if (unlikely(!page_ext))
 		return;
 
-	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
+	page_owner = get_page_owner(page_ext);
+	alloc_handle = page_owner->handle;
+
+	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN, STACK_DEPOT_ACTION_NONE);
 	for (i = 0; i < (1 << order); i++) {
 		__clear_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
 		page_owner = get_page_owner(page_ext);
@@ -153,6 +158,7 @@ void __reset_page_owner(struct page *page, unsigned short order)
 		page_owner->free_ts_nsec = free_ts_nsec;
 		page_ext = page_ext_next(page_ext);
 	}
+	stack_depot_dec_count(alloc_handle);
 }
 
 static inline void __set_page_owner_handle(struct page_ext *page_ext,
@@ -189,7 +195,7 @@ noinline void __set_page_owner(struct page *page, unsigned short order,
 	if (unlikely(!page_ext))
 		return;
 
-	handle = save_stack(gfp_mask);
+	handle = save_stack(gfp_mask, STACK_DEPOT_ACTION_COUNT);
 	__set_page_owner_handle(page_ext, handle, order, gfp_mask);
 }
 
-- 
2.35.3