Cache only a small portion of page map data.

The scudo memory allocator will allocate a large virtual memory address
that causes procrank to allocate a huge amount of data. Modify so it
caches the data a bit at a time.

Remove some allocations that are not necessary since the data is only used
in the first loop.

Fix a few pread64 checks against the actual bytes read, rather than the
read is < 0.

Fix sort by rss in procrank.

Bug: 135694447

Test: Ran unit tests (only one unit test actually runs the modified code).
Test: Ran the old version of procrank using a static libmeminfo and verified
Test: that the same data is found as the new version.

Change-Id: I8adc169b5607ec994ff13a9e161a479350d84c4d
diff --git a/libmeminfo/tools/procrank.cpp b/libmeminfo/tools/procrank.cpp
index cb3757d..1e44ff9 100644
--- a/libmeminfo/tools/procrank.cpp
+++ b/libmeminfo/tools/procrank.cpp
@@ -348,7 +348,7 @@
     auto rss_sort = [](ProcessRecord& a, ProcessRecord& b) {
         MemUsage stats_a = show_wss ? a.Wss() : a.Usage();
         MemUsage stats_b = show_wss ? b.Wss() : b.Usage();
-        return reverse_sort ? stats_a.rss < stats_b.pss : stats_a.pss > stats_b.pss;
+        return reverse_sort ? stats_a.rss < stats_b.rss : stats_a.rss > stats_b.rss;
     };
 
     auto vss_sort = [](ProcessRecord& a, ProcessRecord& b) {