[PATCH] resurrect /proc/meminfo:Buffers

The /proc/meminfo:Buffers statistic is quite useful - it tells us
how effective we are being at caching filesystem metadata.

For example, increases in this figure are a measure of success of the
slablru and buffer_head-limitation patches.

The patch resurrects buffermem accounting.  The metric is calculated
on-demand, via a walk of the blockdev hashtable.

fs/block_dev.c

@@ -332,6 +332,29 @@ struct block_device *bdget(dev_t dev)
 	return bdev;
 }
 
+long nr_blockdev_pages(void)
+{
+	long ret = 0;
+	int i;
+
+	spin_lock(&bdev_lock);
+	for (i = 0; i < ARRAY_SIZE(bdev_hashtable); i++) {
+		struct list_head *head = &bdev_hashtable[i];
+		struct list_head *lh;
+
+		if (head == NULL)
+			continue;
+		list_for_each(lh, head) {
+			struct block_device *bdev;
+
+			bdev = list_entry(lh, struct block_device, bd_hash);
+			ret += bdev->bd_inode->i_mapping->nrpages;
+		}
+	}
+	spin_unlock(&bdev_lock);
+	return ret;
+}
+
 static inline void __bd_forget(struct inode *inode)
 {
 	list_del_init(&inode->i_devices);

fs/proc/proc_misc.c

@@ -165,6 +165,7 @@ static int meminfo_read_proc(char *page, char **start, off_t off,
 		"MemTotal:     %8lu kB\n"
 		"MemFree:      %8lu kB\n"
 		"MemShared:    %8lu kB\n"
+		"Buffers:      %8lu kB\n"
 		"Cached:       %8lu kB\n"
 		"SwapCached:   %8lu kB\n"
 		"Active:       %8lu kB\n"
@@ -185,7 +186,8 @@ static int meminfo_read_proc(char *page, char **start, off_t off,
 		K(i.totalram),
 		K(i.freeram),
 		K(i.sharedram),
-		K(ps.nr_pagecache-swapper_space.nrpages),
+		K(i.bufferram),
+		K(ps.nr_pagecache-swapper_space.nrpages-i.bufferram),
 		K(swapper_space.nrpages),
 		K(active),
 		K(inactive),

include/linux/blkdev.h

@@ -327,7 +327,7 @@ extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bd
 extern int blk_rq_map_sg(request_queue_t *, struct request *, struct scatterlist *);
 extern void blk_dump_rq_flags(struct request *, char *);
 extern void generic_unplug_device(void *);
-
+extern long nr_blockdev_pages(void);
 
 /*
  * tag stuff

mm/page_alloc.c

@@ -23,6 +23,7 @@
 #include <linux/module.h>
 #include <linux/suspend.h>
 #include <linux/pagevec.h>
+#include <linux/blkdev.h>
 
 unsigned long totalram_pages;
 unsigned long totalhigh_pages;
@@ -589,7 +590,7 @@ void si_meminfo(struct sysinfo *val)
 	val->totalram = totalram_pages;
 	val->sharedram = 0;
 	val->freeram = nr_free_pages();
-	val->bufferram = get_page_cache_size();
+	val->bufferram = nr_blockdev_pages();
 #ifdef CONFIG_HIGHMEM
 	val->totalhigh = totalhigh_pages;
 	val->freehigh = nr_free_highpages();