Use an exponential growth strategy for extra blocks.

Change-Id: I4137cb60b79184456aa71d18cb31a52c27bd8792
Reviewed-on: https://skia-review.googlesource.com/9260
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Herb Derby <herb@google.com>

2 files changed, 9 insertions, 1 deletions

diff --git a/src/core/SkArenaAlloc.cpp b/src/core/SkArenaAlloc.cpp
index dee152ae20..779eaff0f1 100644
--- a/src/core/SkArenaAlloc.cpp
+++ b/src/core/SkArenaAlloc.cpp
@@ -100,7 +100,8 @@ void SkArenaAlloc::ensureSpace(uint32_t size, uint32_t alignment) {
         objSizeAndOverhead += alignment - 1;
     }
 
-    uint32_t allocationSize = std::max(objSizeAndOverhead, fExtraSize);
+    uint32_t allocationSize = std::max(objSizeAndOverhead, fExtraSize << fLogGrowth);
+    fLogGrowth++;
 
     // Round up to a nice size. If > 32K align to 4K boundary else up to max_align_t. The > 32K
     // heuristic is from the JEMalloc behavior.
diff --git a/src/core/SkArenaAlloc.h b/src/core/SkArenaAlloc.h
index 3a6fd7d345..04f929181c 100644
--- a/src/core/SkArenaAlloc.h
+++ b/src/core/SkArenaAlloc.h
@@ -52,6 +52,10 @@
 // typical block overhead of 8 bytes. For non-POD objects there is a per item overhead of 4 bytes.
 // For arrays of non-POD objects there is a per array overhead of typically 8 bytes. There is an
 // addition overhead when switching from POD data to non-POD data of typically 8 bytes.
+//
+// If additional blocks are needed they are increased exponentially. This strategy bounds the
+// recursion of the RunDtorsOnBlock to be limited to O(ln size-of-memory). In practical terms, this
+// is a maximum recursion depth of 33 for an 8GB machine but usually much less.
 class SkArenaAlloc {
 public:
     SkArenaAlloc(char* block, size_t size, size_t extraSize = 0);
@@ -192,6 +196,9 @@ private:
     char* const    fFirstBlock;
     const uint32_t fFirstSize;
     const uint32_t fExtraSize;
+    // The extra size allocations grow exponentially:
+    //    size-allocated = extraSize * 2 ^ fLogGrowth.
+    uint8_t        fLogGrowth {0};
 };
 
 #endif//SkFixedAlloc_DEFINED