On 2/12/24 23:30, Oscar Salvador wrote:
> 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.
>
> Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
...
> +static int stack_print(struct seq_file *m, void *v)
> +{
> + char *buf;
> + int ret = 0;
> + struct stack *stack = v;
> + struct stack_record *stack_record = stack->stack_record;
> +
> + if (!stack_record->size || stack_record->size < 0 ||
> + refcount_read(&stack_record->count) < 2)
> + return 0;
> +
> + buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
> +
> + ret += stack_trace_snprint(buf, PAGE_SIZE, stack_record->entries,
> + stack_record->size, 0);
> + if (!ret)
> + goto out;
> +
> + scnprintf(buf + ret, PAGE_SIZE - ret, "stack_count: %d\n\n",
> + refcount_read(&stack_record->count));
> +
> + seq_printf(m, buf);
> + seq_puts(m, "\n\n");
> +out:
> + kfree(buf);
Seems rather wasteful to do kzalloc/kfree so you can print into that buffer
first and then print/copy it again using seq_printf. If you give up on using
stack_trace_snprintf() it's not much harder to print the stack directly with
a loop of seq_printf. See e.g. slab_debugfs_show().
> +
> + return 0;
> +}
> +
