[PATCH] mm/page_alloc: make the annotations of available memory more accurate

[cgel . zte]

From: Yang Yang <yang.yang29@xxxxxxxxxx>

Not all the systems use swap, so estimating available memory would
help to prevent swapping or OOM of system that not use swap.

And we need to reserve some page cache to prevent swapping or
thrashing. If somebody is accessing the pages in pagecache,
and if too much would be freed, most accesses might mean
reading data from disk, i.e. thrashing.

Signed-off-by: Yang Yang <yang.yang29@xxxxxxxxxx>
---
 mm/page_alloc.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e538dde2c1c0..233f68d31cdd 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5889,14 +5889,14 @@ long si_mem_available(void)
 
 	/*
 	 * Estimate the amount of memory available for userspace allocations,
-	 * without causing swapping.
+	 * without causing swapping or OOM.
 	 */
 	available = global_zone_page_state(NR_FREE_PAGES) - totalreserve_pages;
 
 	/*
 	 * 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.
+	 * start swapping or thrashing. Assume at least half of the page
+	 * cache, or the low watermark worth of cache, needs to stay.
 	 */
 	pagecache = pages[LRU_ACTIVE_FILE] + pages[LRU_INACTIVE_FILE];
 	pagecache -= min(pagecache / 2, wmark_low);
-- 
2.25.1