[PATCH] mm: do not consider SWAP to calculate available when not necessary

[Yang Yang <yang.yang29@zte.com.cn>]

When si_mem_available() calculates 'available', it takes SWAP
into account. But if CONFIG_SWAP is N or SWAP is off(some embedded system
would like to do that), there is no need to consider it.

Signed-off-by: Yang Yang <yang.yang29@zte.com.cn>
---
 mm/page_alloc.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6847177..10e186b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4700,6 +4700,7 @@ static inline void show_node(struct zone *zone)
 
 long si_mem_available(void)
 {
+	struct sysinfo i;
 	long available;
 	unsigned long pagecache;
 	unsigned long wmark_low = 0;
@@ -4708,6 +4709,7 @@ long si_mem_available(void)
 	struct zone *zone;
 	int lru;
 
+	si_swapinfo(&i);
 	for (lru = LRU_BASE; lru < NR_LRU_LISTS; lru++)
 		pages[lru] = global_node_page_state(NR_LRU_BASE + lru);
 
@@ -4724,9 +4726,13 @@ long si_mem_available(void)
 	 * Not all the page cache can be freed, otherwise the system will
 	 * start swapping. Assume at least half of the page cache, or the
 	 * low watermark worth of cache, needs to stay.
+	 * But if CONFIG_SWAP is N or SWAP is off, do not consider it.
 	 */
 	pagecache = pages[LRU_ACTIVE_FILE] + pages[LRU_INACTIVE_FILE];
-	pagecache -= min(pagecache / 2, wmark_low);
+#ifdef CONFIG_SWAP
+	if (i.totalswap > 0)
+		pagecache -= min(pagecache / 2, wmark_low);
+#endif
 	available += pagecache;
 
 	/*
-- 
2.15.2