mm: rename and change semantics of nr_indirectly_reclaimable_bytes

The vmstat counter NR_INDIRECTLY_RECLAIMABLE_BYTES was introduced by
commit eb59254608 ("mm: introduce NR_INDIRECTLY_RECLAIMABLE_BYTES") with
the goal of accounting objects that can be reclaimed, but cannot be
allocated via a SLAB_RECLAIM_ACCOUNT cache.  This is now possible via
kmalloc() with __GFP_RECLAIMABLE flag, and the dcache external names user
is converted.

The counter is however still useful for accounting direct page allocations
(i.e.  not slab) with a shrinker, such as the ION page pool.  So keep it,
and:

- change granularity to pages to be more like other counters; sub-page
  allocations should be able to use kmalloc
- rename the counter to NR_KERNEL_MISC_RECLAIMABLE
- expose the counter again in vmstat as "nr_kernel_misc_reclaimable"; we can
  again remove the check for not printing "hidden" counters

Link: http://lkml.kernel.org/r/20180731090649.16028-5-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Christoph Lameter <cl@linux.com>
Acked-by: Roman Gushchin <guro@fb.com>
Cc: Vijayanand Jitta <vjitta@codeaurora.org>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -4701,6 +4701,7 @@ long si_mem_available(void)
 	unsigned long pagecache;
 	unsigned long wmark_low = 0;
 	unsigned long pages[NR_LRU_LISTS];
+	unsigned long reclaimable;
 	struct zone *zone;
 	int lru;
 
@@ -4726,19 +4727,13 @@ long si_mem_available(void)
 	available += pagecache;
 
 	/*
-	 * Part of the reclaimable slab consists of items that are in use,
-	 * and cannot be freed. Cap this estimate at the low watermark.
+	 * Part of the reclaimable slab and other kernel memory consists of
+	 * items that are in use, and cannot be freed. Cap this estimate at the
+	 * low watermark.
 	 */
-	available += global_node_page_state(NR_SLAB_RECLAIMABLE) -
-		     min(global_node_page_state(NR_SLAB_RECLAIMABLE) / 2,
-			 wmark_low);
-
-	/*
-	 * Part of the kernel memory, which can be released under memory
-	 * pressure.
-	 */
-	available += global_node_page_state(NR_INDIRECTLY_RECLAIMABLE_BYTES) >>
-		PAGE_SHIFT;
+	reclaimable = global_node_page_state(NR_SLAB_RECLAIMABLE) +
+			global_node_page_state(NR_KERNEL_MISC_RECLAIMABLE);
+	available += reclaimable - min(reclaimable / 2, wmark_low);
 
 	if (available < 0)
 		available = 0;

mm/util.c

@@ -678,8 +678,7 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
 		 * Part of the kernel memory, which can be released
 		 * under memory pressure.
 		 */
-		free += global_node_page_state(
-			NR_INDIRECTLY_RECLAIMABLE_BYTES) >> PAGE_SHIFT;
+		free += global_node_page_state(NR_KERNEL_MISC_RECLAIMABLE);
 
 		/*
 		 * Leave reserved pages. The pages are not for anonymous pages.

mm/vmstat.c

@@ -1161,7 +1161,7 @@ const char * const vmstat_text[] = {
 	"nr_vmscan_immediate_reclaim",
 	"nr_dirtied",
 	"nr_written",
-	"", /* nr_indirectly_reclaimable */
+	"nr_kernel_misc_reclaimable",
 
 	/* enum writeback_stat_item counters */
 	"nr_dirty_threshold",
@@ -1706,10 +1706,6 @@ static int vmstat_show(struct seq_file *m, void *arg)
 	unsigned long *l = arg;
 	unsigned long off = l - (unsigned long *)m->private;
 
-	/* Skip hidden vmstat items. */
-	if (*vmstat_text[off] == '\0')
-		return 0;
-
 	seq_puts(m, vmstat_text[off]);
 	seq_put_decimal_ull(m, " ", *l);
 	seq_putc(m, '\n');