free: add 'available' memory if provided by the kernel

Show estimated available memory if this is provided by the
kernel. See [1] for the full story.

 [1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=34e431b0ae398fc54ea69ff85ec700722c9da773

function                                             old     new   delta
free_main                                            537     633     +96
parse_cached_kb                                       85       -     -85
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 1/0 up/down: 96/-85)             Total: 11 bytes

Signed-off-by: Guillermo Rodriguez <guille.rodriguez@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 36 insertions, 23 deletions

diff --git a/procps/free.c b/procps/free.c
index 48139c4a3..e41601e08 100644
--- a/procps/free.c
+++ b/procps/free.c
@@ -53,21 +53,27 @@ static unsigned long long scale(struct globals *g, unsigned long d)
 }
 
 /* NOINLINE reduces main() stack usage, which makes code smaller (on x86 at least) */
-static NOINLINE unsigned long parse_cached_kb(void)
+static NOINLINE unsigned int parse_meminfo(unsigned long *cached_kb, unsigned long *available_kb)
 {
         char buf[60]; /* actual lines we expect are ~30 chars or less */
         FILE *fp;
-        unsigned long cached = 0;
+        int seen_cached_and_available;
 
         fp = xfopen_for_read("/proc/meminfo");
-        while (fgets(buf, sizeof(buf), fp) != NULL) {
-                if (sscanf(buf, "Cached: %lu %*s\n", &cached) == 1)
-                        break;
+        *cached_kb = *available_kb = 0;
+        seen_cached_and_available = 2;
+        while (fgets(buf, sizeof(buf), fp)) {
+                if (sscanf(buf, "Cached: %lu %*s\n", cached_kb) == 1)
+                        if (--seen_cached_and_available == 0)
+                                break;
+                if (sscanf(buf, "MemAvailable: %lu %*s\n", available_kb) == 1)
+                        if (--seen_cached_and_available == 0)
+                                break;
         }
         /* Have to close because of NOFORK */
         fclose(fp);
 
-        return cached;
+        return seen_cached_and_available == 0;
 }
 
 int free_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
@@ -75,7 +81,9 @@ int free_main(int argc UNUSED_PARAM, char **argv IF_NOT_DESKTOP(UNUSED_PARAM))
 {
         struct globals G;
         struct sysinfo info;
-        unsigned long long cached;
+        unsigned long long cached, cached_plus_free, available;
+        unsigned long cached_kb, available_kb;
+        int seen_available;
 
 #if ENABLE_DESKTOP
         G.unit_steps = 10;
@@ -98,41 +106,46 @@ int free_main(int argc UNUSED_PARAM, char **argv IF_NOT_DESKTOP(UNUSED_PARAM))
                 }
         }
 #endif
-        printf("       %11s%11s%11s%11s%11s%11s\n"
+        printf("       %12s%12s%12s%12s%12s%12s\n"
         "Mem:   ",
                 "total",
                 "used",
                 "free",
-                "shared", "buffers", "cached" /* swap and total don't have these columns */
+                "shared", "buff/cache", "available" /* swap and total don't have these columns */
         );
 
         sysinfo(&info);
         /* Kernels prior to 2.4.x will return info.mem_unit==0, so cope... */
         G.mem_unit = (info.mem_unit ? info.mem_unit : 1);
-        /* Extract cached from /proc/meminfo and convert to mem_units */
-        cached = ((unsigned long long) parse_cached_kb() * 1024) / G.mem_unit;
+        /* Extract cached and memavailable from /proc/meminfo and convert to mem_units */
+        seen_available = parse_meminfo(&cached_kb, &available_kb);
+        available = ((unsigned long long) available_kb * 1024) / G.mem_unit;
+        cached = ((unsigned long long) cached_kb * 1024) / G.mem_unit;
+        cached += info.bufferram;
+        cached_plus_free = cached + info.freeram;
 
-#define FIELDS_6 "%11llu%11llu%11llu%11llu%11llu%11llu\n"
+#define FIELDS_6 "%12llu%12llu%12llu%12llu%12llu%12llu\n"
 #define FIELDS_3 (FIELDS_6 + 3*6)
 #define FIELDS_2 (FIELDS_6 + 4*6)
 
         printf(FIELDS_6,
                 scale(&G, info.totalram),                //total
-                scale(&G, info.totalram - info.freeram), //used
+                scale(&G, info.totalram - cached_plus_free), //used
                 scale(&G, info.freeram),                 //free
                 scale(&G, info.sharedram),               //shared
-                scale(&G, info.bufferram),               //buffers
-                scale(&G, cached)                        //cached
+                scale(&G, cached),                       //buff/cache
+                scale(&G, available)                     //available
         );
-        /* Show alternate, more meaningful busy/free numbers by counting
+        /* On kernels < 3.14, MemAvailable is not provided.
+         * Show alternate, more meaningful busy/free numbers by counting
          * buffer cache as free memory. */
-        printf("-/+ buffers/cache:");
-        cached += info.freeram;
-        cached += info.bufferram;
-        printf(FIELDS_2,
-                scale(&G, info.totalram - cached), //used
-                scale(&G, cached)                  //free
-        );
+        if (!seen_available) {
+                printf("-/+ buffers/cache: ");
+                printf(FIELDS_2,
+                        scale(&G, info.totalram - cached_plus_free), //used
+                        scale(&G, cached_plus_free)                  //free
+                );
+        }
 #if BB_MMU
         printf("Swap:  ");
         printf(FIELDS_3,