From 765973a098037b198ffb813244dbdb45c875ad5f Mon Sep 17 00:00:00 2001 From: Oscar Salvador Date: Thu, 15 Feb 2024 22:59:05 +0100 Subject: [PATCH] mm,page_owner: display all stacks and their count This patch adds a new directory called 'page_owner_stacks' under /sys/kernel/debug/, with a file called 'show_stacks' in it. Reading from that file will show all stacks that were added by page_owner followed by their counting, giving us a clear overview of stack <-> count relationship. E.g: 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: 4578 The seq stack_{start,next} functions will iterate through the list stack_list in order to print all stacks. Link: https://lkml.kernel.org/r/20240215215907.20121-6-osalvador@suse.de Signed-off-by: Oscar Salvador Acked-by: Marco Elver Reviewed-by: Vlastimil Babka Acked-by: Andrey Konovalov Cc: Alexander Potapenko Cc: Michal Hocko Signed-off-by: Andrew Morton --- mm/page_owner.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 92 insertions(+), 1 deletion(-) diff --git a/mm/page_owner.c b/mm/page_owner.c index df6a923af5de..e99fbf822dd6 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -171,7 +171,13 @@ static void add_stack_record_to_list(struct stack_record *stack_record, spin_lock_irqsave(&stack_list_lock, flags); stack->next = stack_list; - stack_list = stack; + /* + * This pairs with smp_load_acquire() from function + * stack_start(). This guarantees that stack_start() + * will see an updated stack_list before starting to + * traverse the list. + */ + smp_store_release(&stack_list, stack); spin_unlock_irqrestore(&stack_list_lock, flags); } @@ -805,8 +811,90 @@ static const struct file_operations proc_page_owner_operations = { .llseek = lseek_page_owner, }; +static void *stack_start(struct seq_file *m, loff_t *ppos) +{ + struct stack *stack; + + if (*ppos == -1UL) + return NULL; + + if (!*ppos) { + /* + * This pairs with smp_store_release() from function + * add_stack_record_to_list(), so we get a consistent + * value of stack_list. + */ + stack = smp_load_acquire(&stack_list); + } else { + stack = m->private; + stack = stack->next; + } + + m->private = stack; + + return stack; +} + +static void *stack_next(struct seq_file *m, void *v, loff_t *ppos) +{ + struct stack *stack = v; + + stack = stack->next; + *ppos = stack ? *ppos + 1 : -1UL; + m->private = stack; + + return stack; +} + +static int stack_print(struct seq_file *m, void *v) +{ + int i, stack_count; + struct stack *stack = v; + unsigned long *entries; + unsigned long nr_entries; + struct stack_record *stack_record = stack->stack_record; + + nr_entries = stack_record->size; + entries = stack_record->entries; + stack_count = refcount_read(&stack_record->count) - 1; + + if (!nr_entries || nr_entries < 0 || stack_count < 1) + return 0; + + for (i = 0; i < nr_entries; i++) + seq_printf(m, " %pS\n", (void *)entries[i]); + seq_printf(m, "stack_count: %d\n\n", stack_count); + + return 0; +} + +static void stack_stop(struct seq_file *m, void *v) +{ +} + +static const struct seq_operations page_owner_stack_op = { + .start = stack_start, + .next = stack_next, + .stop = stack_stop, + .show = stack_print +}; + +static int page_owner_stack_open(struct inode *inode, struct file *file) +{ + return seq_open_private(file, &page_owner_stack_op, 0); +} + +static const struct file_operations page_owner_stack_operations = { + .open = page_owner_stack_open, + .read = seq_read, + .llseek = seq_lseek, + .release = seq_release, +}; + static int __init pageowner_init(void) { + struct dentry *dir; + if (!static_branch_unlikely(&page_owner_inited)) { pr_info("page_owner is disabled\n"); return 0; @@ -814,6 +902,9 @@ static int __init pageowner_init(void) debugfs_create_file("page_owner", 0400, NULL, NULL, &proc_page_owner_operations); + dir = debugfs_create_dir("page_owner_stacks", NULL); + debugfs_create_file("show_stacks", 0400, dir, NULL, + &page_owner_stack_operations); return 0; }