mm, page_owner: keep owner info when freeing the page

For debugging purposes it might be useful to keep the owner info even
after page has been freed, and include it in e.g.  dump_page() when
detecting a bad page state.  For that, change the PAGE_EXT_OWNER flag
meaning to "page owner info has been set at least once" and add new
PAGE_EXT_OWNER_ACTIVE for tracking whether page is supposed to be
currently tracked allocated or free.  Adjust dump_page() accordingly,
distinguishing free and allocated pages.  In the page_owner debugfs file,
keep printing only allocated pages so that existing scripts are not
confused, and also because free pages are irrelevant for the memory
statistics or leak detection that's the typical use case of the file,
anyway.

Link: http://lkml.kernel.org/r/20190820131828.22684-4-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
index 09592951725cc0b578f356c951348fcc48bfc0ba..682fd465df060c0ac2cde1f67b7b6c11090dd17f 100644 (file)
--- a/include/linux/page_ext.h
+++ b/include/linux/page_ext.h
@@ -18,6 +18,7 @@ struct page_ext_operations {
 
 enum page_ext_flags {
        PAGE_EXT_OWNER,
+       PAGE_EXT_OWNER_ACTIVE,
 #if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
        PAGE_EXT_YOUNG,
        PAGE_EXT_IDLE,

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 813fcb70547b74843d9872816d2fd9a6b3c8c7b4..4a48e018dbdf9603f46592e5aa631bd67ff85dc5 100644 (file)
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -111,7 +111,7 @@ void __reset_page_owner(struct page *page, unsigned int order)
                page_ext = lookup_page_ext(page + i);
                if (unlikely(!page_ext))
                        continue;
-               __clear_bit(PAGE_EXT_OWNER, &page_ext->flags);
+               __clear_bit(PAGE_EXT_OWNER_ACTIVE, &page_ext->flags);
        }
 }
 
@@ -168,6 +168,7 @@ static inline void __set_page_owner_handle(struct page *page,
                page_owner->gfp_mask = gfp_mask;
                page_owner->last_migrate_reason = -1;
                __set_bit(PAGE_EXT_OWNER, &page_ext->flags);
+               __set_bit(PAGE_EXT_OWNER_ACTIVE, &page_ext->flags);
 
                page_ext = lookup_page_ext(page + i);
        }
@@ -243,6 +244,7 @@ void __copy_page_owner(struct page *oldpage, struct page *newpage)
         * the new page, which will be freed.
         */
        __set_bit(PAGE_EXT_OWNER, &new_ext->flags);
+       __set_bit(PAGE_EXT_OWNER_ACTIVE, &new_ext->flags);
 }
 
 void pagetypeinfo_showmixedcount_print(struct seq_file *m,
@@ -302,7 +304,7 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m,
                        if (unlikely(!page_ext))
                                continue;
 
-                       if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags))
+                       if (!test_bit(PAGE_EXT_OWNER_ACTIVE, &page_ext->flags))
                                continue;
 
                        page_owner = get_page_owner(page_ext);
@@ -413,21 +415,26 @@ void __dump_page_owner(struct page *page)
        mt = gfpflags_to_migratetype(gfp_mask);
 
        if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) {
-               pr_alert("page_owner info is not active (free page?)\n");
+               pr_alert("page_owner info is not present (never set?)\n");
                return;
        }
 
+       if (test_bit(PAGE_EXT_OWNER_ACTIVE, &page_ext->flags))
+               pr_alert("page_owner tracks the page as allocated\n");
+       else
+               pr_alert("page_owner tracks the page as freed\n");
+
+       pr_alert("page last allocated via order %u, migratetype %s, gfp_mask %#x(%pGg)\n",
+                page_owner->order, migratetype_names[mt], gfp_mask, &gfp_mask);
+
        handle = READ_ONCE(page_owner->handle);
        if (!handle) {
-               pr_alert("page_owner info is not active (free page?)\n");
-               return;
+               pr_alert("page_owner allocation stack trace missing\n");
+       } else {
+               nr_entries = stack_depot_fetch(handle, &entries);
+               stack_trace_print(entries, nr_entries, 0);
        }
 
-       nr_entries = stack_depot_fetch(handle, &entries);
-       pr_alert("page allocated via order %u, migratetype %s, gfp_mask %#x(%pGg)\n",
-                page_owner->order, migratetype_names[mt], gfp_mask, &gfp_mask);
-       stack_trace_print(entries, nr_entries, 0);
-
        if (page_owner->last_migrate_reason != -1)
                pr_alert("page has been migrated, last migrate reason: %s\n",
                        migrate_reason_names[page_owner->last_migrate_reason]);
@@ -489,6 +496,13 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
                if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags))
                        continue;
 
+               /*
+                * Although we do have the info about past allocation of free
+                * pages, it's not relevant for current memory usage.
+                */
+               if (!test_bit(PAGE_EXT_OWNER_ACTIVE, &page_ext->flags))
+                       continue;
+
                page_owner = get_page_owner(page_ext);
 
                /*