Introduce #private_size.

Author: samuel-williams-shopify

lib/process/metrics/memory.rb

@@ -23,11 +23,30 @@ def total_size
 				self.resident_size + self.swap_size
 			end
 
-			# The unique set size, the size of completely private (unshared) data.
-			def unique_size
+			# The private set size, the size of completely private (unshared) data.
+			# This is the sum of Private_Clean and Private_Dirty pages.
+			# @returns [Integer] Total private memory in bytes.
+			def private_size
 				self.private_clean_size + self.private_dirty_size
 			end
 
+			# The private set size is also known as the unique set size.
+			alias unique_size private_size
+			
+			# The total size of shared (potentially shared with other processes) memory.
+			# This is the sum of Shared_Clean and Shared_Dirty pages.
+			#
+			# When tracking Copy-on-Write (CoW) activity in forked processes:
+			# - Initially, most memory is shared between parent and child.
+			# - As the child writes to memory, CoW triggers and shared pages become private.
+			# - Tracking shared_size decrease vs unique_size increase can indicate CoW activity.
+			# - If shared_size decreases by X and unique_size increases by ~X, it's likely CoW.
+			#
+			# @returns [Integer] Total shared memory in bytes.
+			def shared_size
+				self.shared_clean_size + self.shared_dirty_size
+			end
+			
 			# Create a zero-initialized Memory instance.
 			# @returns [Memory] A new Memory object with all fields set to zero.
 			def self.zero

releases.md

@@ -1,5 +1,9 @@
 # Releases
 
+## Unreleased
+
+  - Add `Process::Metrics::Memory#private_size` for the sum of private (unshared) pages (Private_Clean + Private_Dirty); `#unique_size` is now an alias for `#private_size`.
+
 ## v0.10.1
 
   - Consistent use of `_size` suffix.

test/process/memory.rb

@@ -55,5 +55,20 @@
 				"map_count", "resident_size", "proportional_size", "shared_clean_size", "shared_dirty_size", "private_clean_size", "private_dirty_size", "referenced_size", "anonymous_size", "swap_size", "proportional_swap_size", "minor_faults", "major_faults"
 			)
 		end
+		
+		it "can calculate shared_size and unique_size" do
+			unless memory = capture[pid].memory
+				skip "Detailed memory information is not available on this platform!"
+			end
+			
+			shared_size = memory.shared_size
+			unique_size = memory.unique_size
+			
+			expect(shared_size).to be >= 0
+			expect(unique_size).to be >= 0
+			expect(shared_size).to be == (memory.shared_clean_size + memory.shared_dirty_size)
+			expect(unique_size).to be == (memory.private_clean_size + memory.private_dirty_size)
+			expect(memory.private_size).to be == unique_size
+		end
 	end
 end