2 files changed, 46 insertions, 0 deletions

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 22d89aa37218..8533f5f9bb2d 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -767,6 +767,7 @@ The "Locked" indicates whether the mapping is locked in memory or not.
 
 MemTotal:     16344972 kB
 MemFree:      13634064 kB
+MemAvailable: 14836172 kB
 Buffers:          3656 kB
 Cached:        1195708 kB
 SwapCached:          0 kB
@@ -799,6 +800,14 @@ AnonHugePages:   49152 kB
     MemTotal: Total usable ram (i.e. physical ram minus a few reserved
               bits and the kernel binary code)
      MemFree: The sum of LowFree+HighFree
+MemAvailable: An estimate of how much memory is available for starting new
+              applications, without swapping. Calculated from MemFree,
+              SReclaimable, the size of the file LRU lists, and the low
+              watermarks in each zone.
+              The estimate takes into account that the system needs some
+              page cache to function well, and that not all reclaimable
+              slab will be reclaimable, due to items being in use. The
+              impact of those factors will vary from system to system.
      Buffers: Relatively temporary storage for raw disk blocks
               shouldn't get tremendously large (20MB or so)
       Cached: in-memory cache for files read from the disk (the
diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
index a77d2b299199..24270eceddbf 100644
--- a/fs/proc/meminfo.c
+++ b/fs/proc/meminfo.c
@@ -26,7 +26,11 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
         unsigned long committed;
         struct vmalloc_info vmi;
         long cached;
+        long available;
+        unsigned long pagecache;
+        unsigned long wmark_low = 0;
         unsigned long pages[NR_LRU_LISTS];
+        struct zone *zone;
         int lru;
 
 /*
@@ -47,12 +51,44 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
         for (lru = LRU_BASE; lru < NR_LRU_LISTS; lru++)
                 pages[lru] = global_page_state(NR_LRU_BASE + lru);
 
+        for_each_zone(zone)
+                wmark_low += zone->watermark[WMARK_LOW];
+
+        /*
+         * Estimate the amount of memory available for userspace allocations,
+         * without causing swapping.
+         *
+         * Free memory cannot be taken below the low watermark, before the
+         * system starts swapping.
+         */
+        available = i.freeram - wmark_low;
+
+        /*
+         * 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.
+         */
+        pagecache = pages[LRU_ACTIVE_FILE] + pages[LRU_INACTIVE_FILE];
+        pagecache -= min(pagecache / 2, wmark_low);
+        available += pagecache;
+
+        /*
+         * Part of the reclaimable swap consists of items that are in use,
+         * and cannot be freed. Cap this estimate at the low watermark.
+         */
+        available += global_page_state(NR_SLAB_RECLAIMABLE) -
+                     min(global_page_state(NR_SLAB_RECLAIMABLE) / 2, wmark_low);
+
+        if (available < 0)
+                available = 0;
+
         /*
          * Tagged format, for easy grepping and expansion.
          */
         seq_printf(m,
                 "MemTotal:       %8lu kB\n"
                 "MemFree:        %8lu kB\n"
+                "MemAvailable:   %8lu kB\n"
                 "Buffers:        %8lu kB\n"
                 "Cached:         %8lu kB\n"
                 "SwapCached:     %8lu kB\n"
@@ -105,6 +141,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
                 ,
                 K(i.totalram),
                 K(i.freeram),
+                K(available),
                 K(i.bufferram),
                 K(cached),
                 K(total_swapcache_pages()),