kexec: export PG_swapbacked to VMCOREINFO

Since commit 6326fec ("mm: Use owner_priv bit for PageSwapCache,
valid when PageSwapBacked"), PG_swapcache is an alias for
PG_owner_priv_1, which may be also used for other purposes.

To know whether the bit indeed has the PG_swapcache meaning, it is
necessary to check PG_swapbacked, hence this bit must be exported.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Petr Tesarik <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Cc: Dave Young <[email protected]>
Cc: Xunlei Pang <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Hari Bathini <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: "Marc-Andr Lureau" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/crash_core.c

@@ -454,6 +454,7 @@ static int __init crash_save_vmcoreinfo_init(void)
 	VMCOREINFO_NUMBER(PG_lru);
 	VMCOREINFO_NUMBER(PG_private);
 	VMCOREINFO_NUMBER(PG_swapcache);
+	VMCOREINFO_NUMBER(PG_swapbacked);
 	VMCOREINFO_NUMBER(PG_slab);
 #ifdef CONFIG_MEMORY_FAILURE
 	VMCOREINFO_NUMBER(PG_hwpoison);