summaryrefslogtreecommitdiff
path: root/Documentation
diff options
context:
space:
mode:
authorOscar Salvador <osalvador@suse.de>2024-04-04 09:07:00 +0200
committerAndrew Morton <akpm@linux-foundation.org>2024-04-16 15:39:49 -0700
commitf5c12105c15f0ddf0ff37646290568dd986fa2f3 (patch)
treed4e8271721c9067c1d152fe24be97fa2b8761355 /Documentation
parentea4b5b33bf8a4936cfb07759d926db697c43fb1e (diff)
mm,page_owner: fix refcount imbalance
Current code does not contemplate scenarios were an allocation and free operation on the same pages do not handle it in the same amount at once. To give an example, page_alloc_exact(), where we will allocate a page of enough order to stafisfy the size request, but we will free the remainings right away. In the above example, we will increment the stack_record refcount only once, but we will decrease it the same number of times as number of unused pages we have to free. This will lead to a warning because of refcount imbalance. Fix this by recording the number of base pages in the refcount field. Link: https://lkml.kernel.org/r/20240404070702.2744-3-osalvador@suse.de Reported-by: syzbot+41bbfdb8d41003d12c0f@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-mm/00000000000090e8ff0613eda0e5@google.com Fixes: 217b2119b9e2 ("mm,page_owner: implement the tracking of the stacks count") Signed-off-by: Oscar Salvador <osalvador@suse.de> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Tested-by: Alexandre Ghiti <alexghiti@rivosinc.com> 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: Palmer Dabbelt <palmer@dabbelt.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/mm/page_owner.rst73
1 files changed, 38 insertions, 35 deletions
diff --git a/Documentation/mm/page_owner.rst b/Documentation/mm/page_owner.rst
index 0d0334cd5179..3a45a20fc05a 100644
--- a/Documentation/mm/page_owner.rst
+++ b/Documentation/mm/page_owner.rst
@@ -24,10 +24,10 @@ fragmentation statistics can be obtained through gfp flag information of
each page. It is already implemented and activated if page owner is
enabled. Other usages are more than welcome.
-It can also be used to show all the stacks and their outstanding
-allocations, which gives us a quick overview of where the memory is going
-without the need to screen through all the pages and match the allocation
-and free operation.
+It can also be used to show all the stacks and their current number of
+allocated base pages, which gives us a quick overview of where the memory
+is going without the need to screen through all the pages and match the
+allocation and free operation.
page owner is disabled by default. So, if you'd like to use it, you need
to add "page_owner=on" to your boot cmdline. If the kernel is built
@@ -75,42 +75,45 @@ Usage
cat /sys/kernel/debug/page_owner_stacks/show_stacks > stacks.txt
cat stacks.txt
- prep_new_page+0xa9/0x120
- get_page_from_freelist+0x7e6/0x2140
- __alloc_pages+0x18a/0x370
- new_slab+0xc8/0x580
- ___slab_alloc+0x1f2/0xaf0
- __slab_alloc.isra.86+0x22/0x40
- kmem_cache_alloc+0x31b/0x350
- __khugepaged_enter+0x39/0x100
- dup_mmap+0x1c7/0x5ce
- copy_process+0x1afe/0x1c90
- kernel_clone+0x9a/0x3c0
- __do_sys_clone+0x66/0x90
- do_syscall_64+0x7f/0x160
- entry_SYSCALL_64_after_hwframe+0x6c/0x74
- stack_count: 234
+ post_alloc_hook+0x177/0x1a0
+ get_page_from_freelist+0xd01/0xd80
+ __alloc_pages+0x39e/0x7e0
+ allocate_slab+0xbc/0x3f0
+ ___slab_alloc+0x528/0x8a0
+ kmem_cache_alloc+0x224/0x3b0
+ sk_prot_alloc+0x58/0x1a0
+ sk_alloc+0x32/0x4f0
+ inet_create+0x427/0xb50
+ __sock_create+0x2e4/0x650
+ inet_ctl_sock_create+0x30/0x180
+ igmp_net_init+0xc1/0x130
+ ops_init+0x167/0x410
+ setup_net+0x304/0xa60
+ copy_net_ns+0x29b/0x4a0
+ create_new_namespaces+0x4a1/0x820
+ nr_base_pages: 16
...
...
echo 7000 > /sys/kernel/debug/page_owner_stacks/count_threshold
cat /sys/kernel/debug/page_owner_stacks/show_stacks> stacks_7000.txt
cat stacks_7000.txt
- prep_new_page+0xa9/0x120
- get_page_from_freelist+0x7e6/0x2140
- __alloc_pages+0x18a/0x370
- alloc_pages_mpol+0xdf/0x1e0
- folio_alloc+0x14/0x50
- filemap_alloc_folio+0xb0/0x100
- page_cache_ra_unbounded+0x97/0x180
- filemap_fault+0x4b4/0x1200
- __do_fault+0x2d/0x110
- do_pte_missing+0x4b0/0xa30
- __handle_mm_fault+0x7fa/0xb70
- handle_mm_fault+0x125/0x300
- do_user_addr_fault+0x3c9/0x840
- exc_page_fault+0x68/0x150
- asm_exc_page_fault+0x22/0x30
- stack_count: 8248
+ post_alloc_hook+0x177/0x1a0
+ get_page_from_freelist+0xd01/0xd80
+ __alloc_pages+0x39e/0x7e0
+ alloc_pages_mpol+0x22e/0x490
+ folio_alloc+0xd5/0x110
+ filemap_alloc_folio+0x78/0x230
+ page_cache_ra_order+0x287/0x6f0
+ filemap_get_pages+0x517/0x1160
+ filemap_read+0x304/0x9f0
+ xfs_file_buffered_read+0xe6/0x1d0 [xfs]
+ xfs_file_read_iter+0x1f0/0x380 [xfs]
+ __kernel_read+0x3b9/0x730
+ kernel_read_file+0x309/0x4d0
+ __do_sys_finit_module+0x381/0x730
+ do_syscall_64+0x8d/0x150
+ entry_SYSCALL_64_after_hwframe+0x62/0x6a
+ nr_base_pages: 20824
...
cat /sys/kernel/debug/page_owner > page_owner_full.txt