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@xxxxxxx>
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@xxxxxxx
Link: https://lkml.kernel.org/r/20240212223029.30769-2-osalvador@xxxxxxx
Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxx 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
