tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index b94d38b37fe23f032008473843f1182ff71f17ba..65d29aff2c454f63c3d6c54ae096cef5eba33ac8 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -18458,6 +18458,50 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Platform.ZramCompressedSize" units="MB">
+  <owner>semenzato@google.com</owner>
+  <summary>
+    Compressed swap size in megabytes.  This is the actual amount of RAM used by
+    the system to compress memory (i.e. after compression).  Snapshot every 30s.
+  </summary>
+</histogram>
+
+<histogram name="Platform.ZramCompressionRatioPercent" units="%">
+  <owner>semenzato@google.com</owner>
+  <summary>
+    Compression ratio in percents (between 100% and 600%, i.e. a ratio between 1

[Ilya Sherman, 2014/06/11 20:30:47]

Hmm, why is 600% the upper bound, and why is 100% the lower bound?  IMO your
metric would be clearer if it were typically a number between 0% and 100%, i.e.
if you reversed the numerator and denominator.  Keep in mind also that
compression can, in principle, actually be *worse* than no compression, i.e. the
compressed size can be greater than the uncompressed size.

+    and 6) when the compressed memory is at least 1 MB after compression. This
+    is the fraction of RAM used before compression (including zero pages) and
+    after compression.  Values close to 100% indicate low compression
+    effectiveness. Snapshot every 30s.

[Ilya Sherman, 2014/06/11 21:37:30]

nit: Suggested phrasing tweaks, that help at least me to more quickly understand
the prose.  Feel free to further refine.

"Compression ratio, expressed as a percentage (typically between 100% and 600%,
i.e. a ratio between 1 and 6), when the compressed memory is at least 1 MB after
compression.  This is the ratio of the RAM used before compression (including
zero pages) to the RAM used after compression.  Values close to 100% indicate
low compression effectiveness. Snapshot every 30s."

+  </summary>
+</histogram>
+
+<histogram name="Platform.ZramSavings" units="MB">
+  <owner>semenzato@google.com</owner>
+  <summary>
+    RAM savings in megabytes from using memory compression.  This is the
+    difference between the RAM size before and after compression.  Snapshot
+    every 30s.
+  </summary>
+</histogram>
+
+<histogram name="Platform.ZramZeroPages" units="pages">
+  <owner>semenzato@google.com</owner>
+  <summary>
+    Number of zero-filled pages that the OS is compressing.  A large number
+    suggests wasteful allocation.  Snapshot every 30s.
+  </summary>
+</histogram>
+
+<histogram name="Platform.ZramZeroRatioPercent" units="%">
+  <owner>semenzato@google.com</owner>
+  <summary>
+    The fraction of compressed memory that consists of zero-filled pages.
+    Snapshot every 30s.
+  </summary>
+</histogram>
+
 <histogram name="PlatformFile.UnknownCreateFileErrors" units="code">
   <obsolete>
     Deprecated as of 2013-05, replaced by