mm/page_owner: add debugfs file 'show_stacks_handles'

Add the file 'show_stacks_handles' to show just stack traces and their
handles, in order to resolve stack traces and handles (i.e., to identify
the stack traces for handles in previous reads from 'show_handles').

All stacks/handles must show up, regardless of their number of pages, that
might have become zero or no longer make 'count_threshold', but made it in
previous reads from 'show_handles' -- and need to be resolved later.

P.S.: now, print the extra newline independently of the number of pages.

Link: https://lkml.kernel.org/r/20251001175611.575861-5-mfo@igalia.com
Signed-off-by: Mauricio Faria de Oliveira <mfo@igalia.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/page_owner.c b/mm/page_owner.c
index fe788f07b57875af96f805f5ac139384264304d4..9c67bb8fb1d9d3990d6457b322fc01a28443099b 100644 (file)
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -916,7 +916,8 @@ static int stack_print(struct seq_file *m, void *v)
 
        nr_base_pages = refcount_read(&stack_record->count) - 1;
 
-       if (nr_base_pages < 1 || nr_base_pages < page_owner_pages_threshold)
+       if (ctx->flags & STACK_PRINT_FLAG_PAGES &&
+           (nr_base_pages < 1 || nr_base_pages < page_owner_pages_threshold))
                return 0;
 
        if (ctx->flags & STACK_PRINT_FLAG_STACK) {
@@ -928,7 +929,8 @@ static int stack_print(struct seq_file *m, void *v)
        if (ctx->flags & STACK_PRINT_FLAG_HANDLE)
                seq_printf(m, "handle: %d\n", stack_record->handle.handle);
        if (ctx->flags & STACK_PRINT_FLAG_PAGES)
-               seq_printf(m, "nr_base_pages: %d\n\n", nr_base_pages);
+               seq_printf(m, "nr_base_pages: %d\n", nr_base_pages);
+       seq_putc(m, '\n');
 
        return 0;
 }
@@ -1002,6 +1004,10 @@ static int __init pageowner_init(void)
                            (void *)(STACK_PRINT_FLAG_HANDLE |
                                     STACK_PRINT_FLAG_PAGES),
                            &page_owner_stack_operations);
+       debugfs_create_file("show_stacks_handles", 0400, dir,
+                           (void *)(STACK_PRINT_FLAG_STACK |
+                                    STACK_PRINT_FLAG_HANDLE),
+                           &page_owner_stack_operations);
        debugfs_create_file("count_threshold", 0600, dir, NULL,
                            &proc_page_owner_threshold);