Modernize getAvailableMemoryKB for linux

Signed-off-by: Rye <[email protected]>

Author: RyeMutt

indra/llcommon/llsys.cpp

@@ -822,57 +822,8 @@ void LLMemoryInfo::getAvailableMemoryKB(U32Kilobytes& avail_mem_kb)
     }
 
 #elif LL_LINUX
-    // mStatsMap is derived from MEMINFO_FILE:
-    // $ cat /proc/meminfo
-    // MemTotal:        4108424 kB
-    // MemFree:         1244064 kB
-    // Buffers:           85164 kB
-    // Cached:          1990264 kB
-    // SwapCached:            0 kB
-    // Active:          1176648 kB
-    // Inactive:        1427532 kB
-    // Active(anon):     529152 kB
-    // Inactive(anon):    15924 kB
-    // Active(file):     647496 kB
-    // Inactive(file):  1411608 kB
-    // Unevictable:          16 kB
-    // Mlocked:              16 kB
-    // HighTotal:       3266316 kB
-    // HighFree:         721308 kB
-    // LowTotal:         842108 kB
-    // LowFree:          522756 kB
-    // SwapTotal:       6384632 kB
-    // SwapFree:        6384632 kB
-    // Dirty:                28 kB
-    // Writeback:             0 kB
-    // AnonPages:        528820 kB
-    // Mapped:            89472 kB
-    // Shmem:             16324 kB
-    // Slab:             159624 kB
-    // SReclaimable:     145168 kB
-    // SUnreclaim:        14456 kB
-    // KernelStack:        2560 kB
-    // PageTables:         5560 kB
-    // NFS_Unstable:          0 kB
-    // Bounce:                0 kB
-    // WritebackTmp:          0 kB
-    // CommitLimit:     8438844 kB
-    // Committed_AS:    1271596 kB
-    // VmallocTotal:     122880 kB
-    // VmallocUsed:       65252 kB
-    // VmallocChunk:      52356 kB
-    // HardwareCorrupted:     0 kB
-    // HugePages_Total:       0
-    // HugePages_Free:        0
-    // HugePages_Rsvd:        0
-    // HugePages_Surp:        0
-    // Hugepagesize:       2048 kB
-    // DirectMap4k:      434168 kB
-    // DirectMap2M:      477184 kB
-    // (could also run 'free', but easier to read a file than run a program)
-    LLSD statsMap(loadStatsMap());
-
-    avail_mem_kb = (U32Kilobytes)statsMap["MemFree"].asInteger();
+    U64 phys = U64(getpagesize()) * U64(get_avphys_pages());
+    avail_mem_kb = U64Bytes(phys);
 #else
     //do not know how to collect available memory info for other systems.
     //leave it blank here for now.