mm,thp: stats for file backed THP

In preparation for non-shmem THP, this patch adds a few stats and exposes
them in /proc/meminfo, /sys/bus/node/devices/<node>/meminfo, and
/proc/<pid>/task/<tid>/smaps.

This patch is mostly a rewrite of Kirill A. Shutemov's earlier version:
https://lkml.kernel.org/r/[e-mail]/

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Song Liu <[e-mail]>
Acked-by: Rik van Riel <[e-mail]>
Acked-by: Kirill A. Shutemov <[e-mail]>
Acked-by: Johannes Weiner <[e-mail]>
Cc: Hillf Danton <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: William Kucharski <[e-mail]>
Cc: Oleg Nesterov <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/base/node.c

···
 		       "Node %d AnonHugePages:  %8lu kB\n"
 		       "Node %d ShmemHugePages: %8lu kB\n"
 		       "Node %d ShmemPmdMapped: %8lu kB\n"
+		       "Node %d FileHugePages: %8lu kB\n"
+		       "Node %d FilePmdMapped: %8lu kB\n"
 #endif
 			,
 		       nid, K(node_page_state(pgdat, NR_FILE_DIRTY)),
···
 		       nid, K(node_page_state(pgdat, NR_SHMEM_THPS) *
 				       HPAGE_PMD_NR),
 		       nid, K(node_page_state(pgdat, NR_SHMEM_PMDMAPPED) *
+				       HPAGE_PMD_NR),
+		       nid, K(node_page_state(pgdat, NR_FILE_THPS) *
+				       HPAGE_PMD_NR),
+		       nid, K(node_page_state(pgdat, NR_FILE_PMDMAPPED) *
 				       HPAGE_PMD_NR)
 #endif
 		       );

fs/proc/meminfo.c

···
 		    global_node_page_state(NR_SHMEM_THPS) * HPAGE_PMD_NR);
 	show_val_kb(m, "ShmemPmdMapped: ",
 		    global_node_page_state(NR_SHMEM_PMDMAPPED) * HPAGE_PMD_NR);
+	show_val_kb(m, "FileHugePages: ",
+		    global_node_page_state(NR_FILE_THPS) * HPAGE_PMD_NR);
+	show_val_kb(m, "FilePmdMapped: ",
+		    global_node_page_state(NR_FILE_PMDMAPPED) * HPAGE_PMD_NR);
 #endif
 
 #ifdef CONFIG_CMA

fs/proc/task_mmu.c

···
 	unsigned long lazyfree;
 	unsigned long anonymous_thp;
 	unsigned long shmem_thp;
+	unsigned long file_thp;
 	unsigned long swap;
 	unsigned long shared_hugetlb;
 	unsigned long private_hugetlb;
···
 	else if (is_zone_device_page(page))
 		/* pass */;
 	else
-		VM_BUG_ON_PAGE(1, page);
+		mss->file_thp += HPAGE_PMD_SIZE;
 	smaps_account(mss, page, true, pmd_young(*pmd), pmd_dirty(*pmd), locked);
 }
 #else
···
 	SEQ_PUT_DEC(" kB\nLazyFree:       ", mss->lazyfree);
 	SEQ_PUT_DEC(" kB\nAnonHugePages:  ", mss->anonymous_thp);
 	SEQ_PUT_DEC(" kB\nShmemPmdMapped: ", mss->shmem_thp);
+	SEQ_PUT_DEC(" kB\nFilePmdMapped: ", mss->file_thp);
 	SEQ_PUT_DEC(" kB\nShared_Hugetlb: ", mss->shared_hugetlb);
 	seq_put_decimal_ull_width(m, " kB\nPrivate_Hugetlb: ",
 				  mss->private_hugetlb >> 10, 7);

include/linux/mmzone.h

···
 	NR_SHMEM,		/* shmem pages (included tmpfs/GEM pages) */
 	NR_SHMEM_THPS,
 	NR_SHMEM_PMDMAPPED,
+	NR_FILE_THPS,
+	NR_FILE_PMDMAPPED,
 	NR_ANON_THPS,
 	NR_UNSTABLE_NFS,	/* NFS unstable pages */
 	NR_VMSCAN_WRITE,

mm/vmstat.c

···
 	"nr_shmem",
 	"nr_shmem_hugepages",
 	"nr_shmem_pmdmapped",
+	"nr_file_hugepages",
+	"nr_file_pmdmapped",
 	"nr_anon_transparent_hugepages",
 	"nr_unstable",
 	"nr_vmscan_write",