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

[Yang Yang]

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.yan...@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