[PATCH] buffermem_pages removal (4/5)

This is the most discussion-worthy patch of the series:  Change the
meaning of si_meminfo->bufferram from "all pages in pagecache
backed by block devices" to "all pages in pagecache".

In the header/manpage is is documented as "Memory used by buffers",
but as the buffercache is gone I think the new meaning fits the
intention from pre-pagecache days much better.

mm/page_alloc.c

@@ -613,7 +613,7 @@ void si_meminfo(struct sysinfo *val)
 	val->totalram = totalram_pages;
 	val->sharedram = 0;
 	val->freeram = nr_free_pages();
-	val->bufferram = atomic_read(&buffermem_pages);
+	val->bufferram = get_page_cache_size();
 #ifdef CONFIG_HIGHMEM
 	val->totalhigh = totalhigh_pages;
 	val->freehigh = nr_free_highpages();