+ lib-stackdepot-move-stack_record-struct-definition-into-the-header.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: lib/stackdepot: move stack_record struct definition into the header
has been added to the -mm mm-unstable branch.  Its filename is
     lib-stackdepot-move-stack_record-struct-definition-into-the-header.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/lib-stackdepot-move-stack_record-struct-definition-into-the-header.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Oscar Salvador <osalvador@suse.de>
Subject: lib/stackdepot: move stack_record struct definition into the header
Date: Mon, 12 Feb 2024 23:30:25 +0100

Patch eries "page_owner: print stacks and their outstanding allocations",
v8.

page_owner is a great debug functionality tool that lets us know about all
pages that have been allocated/freed and their specific stacktrace.  This
comes in very handy when debugging memory leaks, since with some scripting
we can see the outstanding allocations, which might point to a memory
leak.

In my experience, that is one of the most useful cases, but it can get
really tedious to screen through all pages and try to reconstruct the
stack <-> allocated/freed relationship, becoming most of the time a
daunting and slow process when we have tons of allocation/free operations.
 

This patchset aims to ease that by adding a new functionality into
page_owner.  This functionality creates a new directory called
'page_owner_stacks' under 'sys/kernel//debug' with a read-only file called
'show_stacks', which prints out all the stacks followed by their
outstanding number of allocations (being that the times the stacktrace has
allocated but not freed yet).  This gives us a clear and a quick overview
of stacks <-> allocated/free.

We take advantage of the new refcount_f field that stack_record struct
gained, and increment/decrement the stack refcount on every
__set_page_owner() (alloc operation) and __reset_page_owner (free
operation) call.

Unfortunately, we cannot use the new stackdepot api
STACK_DEPOT_FLAG_{GET,PUT} because it does not fulfill page_owner needs,
meaning we would have to special case things, at which point makes more
sense for page_owner to do its own {dec,inc}rementing of the stacks.  E.g:
Using STACK_DEPOT_FLAG_PUT, once the refcount reaches 0, such stack gets
evicted, so page_owner would lose information.

This patch also creates a new file called 'set_threshold' within
'page_owner_stacks' directory, and by writing a value to it, the stacks
which refcount is below such value will be filtered out.

A PoC can be found below:

 # cat /sys/kernel/debug/page_owner_stacks/show_stacks > page_owner_full_stacks.txt
 # head -40 page_owner_full_stacks.txt 
  prep_new_page+0xa9/0x120
  get_page_from_freelist+0x801/0x2210
  __alloc_pages+0x18b/0x350
  alloc_pages_mpol+0x91/0x1f0
  folio_alloc+0x14/0x50
  filemap_alloc_folio+0xb2/0x100
  page_cache_ra_unbounded+0x96/0x180
  filemap_get_pages+0xfd/0x590
  filemap_read+0xcc/0x330
  blkdev_read_iter+0xb8/0x150
  vfs_read+0x285/0x320
  ksys_read+0xa5/0xe0
  do_syscall_64+0x80/0x160
  entry_SYSCALL_64_after_hwframe+0x6e/0x76
 stack_count: 521



  prep_new_page+0xa9/0x120
  get_page_from_freelist+0x801/0x2210
  __alloc_pages+0x18b/0x350
  alloc_pages_mpol+0x91/0x1f0
  folio_alloc+0x14/0x50
  filemap_alloc_folio+0xb2/0x100
  __filemap_get_folio+0x14a/0x490
  ext4_write_begin+0xbd/0x4b0 [ext4]
  generic_perform_write+0xc1/0x1e0
  ext4_buffered_write_iter+0x68/0xe0 [ext4]
  ext4_file_write_iter+0x70/0x740 [ext4]
  vfs_write+0x33d/0x420
  ksys_write+0xa5/0xe0
  do_syscall_64+0x80/0x160
  entry_SYSCALL_64_after_hwframe+0x6e/0x76
 stack_count: 4609
...
...

 # echo 5000 > /sys/kernel/debug/page_owner_stacks/set_threshold 
 # cat /sys/kernel/debug/page_owner_stacks/show_stacks > page_owner_full_stacks_5000.txt
 # head -40 page_owner_full_stacks_5000.txt 
  prep_new_page+0xa9/0x120
  get_page_from_freelist+0x801/0x2210
  __alloc_pages+0x18b/0x350
  alloc_pages_mpol+0x91/0x1f0
  folio_alloc+0x14/0x50
  filemap_alloc_folio+0xb2/0x100
  __filemap_get_folio+0x14a/0x490
  ext4_write_begin+0xbd/0x4b0 [ext4]
  generic_perform_write+0xc1/0x1e0
  ext4_buffered_write_iter+0x68/0xe0 [ext4]
  ext4_file_write_iter+0x70/0x740 [ext4]
  vfs_write+0x33d/0x420
  ksys_pwrite64+0x75/0x90
  do_syscall_64+0x80/0x160
  entry_SYSCALL_64_after_hwframe+0x6e/0x76
 stack_count: 6781



  prep_new_page+0xa9/0x120
  get_page_from_freelist+0x801/0x2210
  __alloc_pages+0x18b/0x350
  pcpu_populate_chunk+0xec/0x350
  pcpu_balance_workfn+0x2d1/0x4a0
  process_scheduled_works+0x84/0x380
  worker_thread+0x12a/0x2a0
  kthread+0xe3/0x110
  ret_from_fork+0x30/0x50
  ret_from_fork_asm+0x1b/0x30
 stack_count: 8641


This patch (of 5):

In order to move the heavy lifting into page_owner code, this one needs to
have access to the stack_record structure, which right now sits in
lib/stackdepot.c.  Move it to the stackdepot.h header so page_owner can
access stack_record's struct fields.

Link: https://lkml.kernel.org/r/20240212223029.30769-1-osalvador@suse.de
Link: https://lkml.kernel.org/r/20240212223029.30769-2-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Marco Elver <elver@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/stackdepot.h |   44 +++++++++++++++++++++++++++++++++++
 lib/stackdepot.c           |   43 ----------------------------------
 2 files changed, 44 insertions(+), 43 deletions(-)

--- a/include/linux/stackdepot.h~lib-stackdepot-move-stack_record-struct-definition-into-the-header
+++ a/include/linux/stackdepot.h
@@ -30,6 +30,50 @@ typedef u32 depot_stack_handle_t;
  */
 #define STACK_DEPOT_EXTRA_BITS 5
 
+#define DEPOT_HANDLE_BITS (sizeof(depot_stack_handle_t) * 8)
+
+#define DEPOT_POOL_ORDER 2 /* Pool size order, 4 pages */
+#define DEPOT_POOL_SIZE (1LL << (PAGE_SHIFT + DEPOT_POOL_ORDER))
+#define DEPOT_STACK_ALIGN 4
+#define DEPOT_OFFSET_BITS (DEPOT_POOL_ORDER + PAGE_SHIFT - DEPOT_STACK_ALIGN)
+#define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_OFFSET_BITS - \
+			       STACK_DEPOT_EXTRA_BITS)
+
+/* Compact structure that stores a reference to a stack. */
+union handle_parts {
+	depot_stack_handle_t handle;
+	struct {
+		u32 pool_index	: DEPOT_POOL_INDEX_BITS;
+		u32 offset	: DEPOT_OFFSET_BITS;
+		u32 extra	: STACK_DEPOT_EXTRA_BITS;
+	};
+};
+
+struct stack_record {
+	struct list_head hash_list;	/* Links in the hash table */
+	u32 hash;			/* Hash in hash table */
+	u32 size;			/* Number of stored frames */
+	union handle_parts handle;	/* Constant after initialization */
+	refcount_t count;
+	union {
+		unsigned long entries[CONFIG_STACKDEPOT_MAX_FRAMES];	/* Frames */
+		struct {
+			/*
+			 * An important invariant of the implementation is to
+			 * only place a stack record onto the freelist iff its
+			 * refcount is zero. Because stack records with a zero
+			 * refcount are never considered as valid, it is safe to
+			 * union @entries and freelist management state below.
+			 * Conversely, as soon as an entry is off the freelist
+			 * and its refcount becomes non-zero, the below must not
+			 * be accessed until being placed back on the freelist.
+			 */
+			struct list_head free_list;	/* Links in the freelist */
+			unsigned long rcu_state;	/* RCU cookie */
+		};
+	};
+};
+
 typedef u32 depot_flags_t;
 
 /*
--- a/lib/stackdepot.c~lib-stackdepot-move-stack_record-struct-definition-into-the-header
+++ a/lib/stackdepot.c
@@ -36,54 +36,11 @@
 #include <linux/memblock.h>
 #include <linux/kasan-enabled.h>
 
-#define DEPOT_HANDLE_BITS (sizeof(depot_stack_handle_t) * 8)
-
-#define DEPOT_POOL_ORDER 2 /* Pool size order, 4 pages */
-#define DEPOT_POOL_SIZE (1LL << (PAGE_SHIFT + DEPOT_POOL_ORDER))
-#define DEPOT_STACK_ALIGN 4
-#define DEPOT_OFFSET_BITS (DEPOT_POOL_ORDER + PAGE_SHIFT - DEPOT_STACK_ALIGN)
-#define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_OFFSET_BITS - \
-			       STACK_DEPOT_EXTRA_BITS)
 #define DEPOT_POOLS_CAP 8192
 #define DEPOT_MAX_POOLS \
 	(((1LL << (DEPOT_POOL_INDEX_BITS)) < DEPOT_POOLS_CAP) ? \
 	 (1LL << (DEPOT_POOL_INDEX_BITS)) : DEPOT_POOLS_CAP)
 
-/* Compact structure that stores a reference to a stack. */
-union handle_parts {
-	depot_stack_handle_t handle;
-	struct {
-		u32 pool_index	: DEPOT_POOL_INDEX_BITS;
-		u32 offset	: DEPOT_OFFSET_BITS;
-		u32 extra	: STACK_DEPOT_EXTRA_BITS;
-	};
-};
-
-struct stack_record {
-	struct list_head hash_list;	/* Links in the hash table */
-	u32 hash;			/* Hash in hash table */
-	u32 size;			/* Number of stored frames */
-	union handle_parts handle;	/* Constant after initialization */
-	refcount_t count;
-	union {
-		unsigned long entries[CONFIG_STACKDEPOT_MAX_FRAMES];	/* Frames */
-		struct {
-			/*
-			 * An important invariant of the implementation is to
-			 * only place a stack record onto the freelist iff its
-			 * refcount is zero. Because stack records with a zero
-			 * refcount are never considered as valid, it is safe to
-			 * union @entries and freelist management state below.
-			 * Conversely, as soon as an entry is off the freelist
-			 * and its refcount becomes non-zero, the below must not
-			 * be accessed until being placed back on the freelist.
-			 */
-			struct list_head free_list;	/* Links in the freelist */
-			unsigned long rcu_state;	/* RCU cookie */
-		};
-	};
-};
-
 static bool stack_depot_disabled;
 static bool __stack_depot_early_init_requested __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT);
 static bool __stack_depot_early_init_passed __initdata;
_

Patches currently in -mm which might be from osalvador@suse.de are

lib-stackdepot-move-stack_record-struct-definition-into-the-header.patch
mmpage_owner-implement-the-tracking-of-the-stacks-count.patch
mmpage_owner-display-all-stacks-and-their-count.patch
mmpage_owner-filter-out-stacks-by-a-threshold.patch
mmpage_owner-update-documentation-regarding-page_owner_stacks.patch