ANDROID: mm: introduce page_pinner
For CMA allocation, it's really critical to migrate a page but
sometimes it fails. One of the reasons is some driver holds a
page refcount for a long time so VM couldn't migrate the page
at that time.
The concern here is there is no way to find the who hold the
refcount of the page effectively. This patch introduces feature
to keep tracking page's pinner. All get_page sites are vulnerable
to pin a page for a long time but the cost to keep track it would
be significat since get_page is the most frequent kernel operation.
Furthermore, the page could be not user page but kernel page which
is not related to the page migration failure.
Thus, this patch keeps tracks of only migration failed pages to
reduce runtime cost. Once page migration fails in CMA allocation
path, those pages are marked as "migration failure" and every
put_page operation against those pages, callstack of the put
are recorded into page_pinner buffer. Later, admin can see
what pages were failed and who released the refcount since the
failure. It really helps effectively to find out longtime refcount
holder to prevent the page migration.
note: page_pinner doesn't guarantee attributing/unattributing are
atomic if they happen at the same time. It's just best effort so
false-positive could happen.
Bug: 183414571
BUg: 240196534
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Minchan Kim <minchan@google.com>
Change-Id: I603d0c0122734c377db6b1eb95848a6f734173a0
(cherry picked from commit 898cfbf094a2fc13c67fab5b5d3c916f0139833a)
diff --git a/mm/page_ext.c b/mm/page_ext.c
index cc52014..4f81320 100644
--- a/mm/page_ext.c
+++ b/mm/page_ext.c
@@ -7,6 +7,7 @@
#include <linux/vmalloc.h>
#include <linux/kmemleak.h>
#include <linux/page_owner.h>
+#include <linux/page_pinner.h>
#include <linux/page_idle.h>
/*
@@ -75,6 +76,9 @@ static struct page_ext_operations *page_ext_ops[] = {
#if defined(CONFIG_PAGE_IDLE_FLAG) && !defined(CONFIG_64BIT)
&page_idle_ops,
#endif
+#ifdef CONFIG_PAGE_PINNER
+ &page_pinner_ops,
+#endif
};
unsigned long page_ext_size = sizeof(struct page_ext);