From: Vlastimil Babka <vbabka@suse.cz>
Date: Mon, 23 Sep 2019 15:34:39 -0700
Subject: mm, page_owner: keep owner info when freeing the page
Git-commit: 37389167a281f3ccb6bc958c32b2e088c7269fe0
Patch-mainline: v5.4-rc1
References: jsc#SLE-8956, bsc#1144653, VM Debug Functionality

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>
---
 include/linux/page_ext.h |    1 +
 mm/page_owner.c          |   34 ++++++++++++++++++++++++----------
 2 files changed, 25 insertions(+), 10 deletions(-)

--- a/include/linux/page_ext.h
+++ b/include/linux/page_ext.h
@@ -29,6 +29,7 @@ enum page_ext_flags {
 	PAGE_EXT_DEBUG_POISON,		/* Page is poisoned */
 	PAGE_EXT_DEBUG_GUARD,
 	PAGE_EXT_OWNER,
+	PAGE_EXT_OWNER_ACTIVE,
 #if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
 	PAGE_EXT_YOUNG,
 	PAGE_EXT_IDLE,
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -115,7 +115,7 @@ void __reset_page_owner(struct page *pag
 		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);
 	}
 }
 
@@ -182,6 +182,7 @@ static inline void __set_page_owner_hand
 		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);
 	}
@@ -257,6 +258,7 @@ void __copy_page_owner(struct page *oldp
 	 * 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,
@@ -312,7 +314,7 @@ void pagetypeinfo_showmixedcount_print(s
 			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);
@@ -433,21 +435,26 @@ 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 {
+		depot_fetch_stack(handle, &trace);
+		print_stack_trace(&trace, 0);
 	}
 
-	depot_fetch_stack(handle, &trace);
-	pr_alert("page allocated via order %u, migratetype %s, gfp_mask %#x(%pGg)\n",
-		 page_owner->order, migratetype_names[mt], gfp_mask, &gfp_mask);
-	print_stack_trace(&trace, 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]);
@@ -509,6 +516,13 @@ read_page_owner(struct file *file, char
 		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);
 
 		/*