linker: Purge block allocator memory when possible

If all allocated memory from a block allocator is freed, it is a good
opportunity to purge all the pages allocated to reduce lingering dirty
pages.

Memory saving varies with the platform and what processes are running.
Measuring right after boot, this saves ~1.8MB on cuttelfish and ~1.3MB
on a 32-bit ARM device.

Bug: 112073665
Test: Boot and check memory usage with 'showmap'.
Change-Id: I53769e0ec9699f0b3645cdf281a2c0bbffb98676

1 files changed, 4 insertions, 1 deletions

diff --git a/linker/linker_block_allocator.h b/linker/linker_block_allocator.h
index bd44fc829..85e6bd962 100644
--- a/linker/linker_block_allocator.h
+++ b/linker/linker_block_allocator.h
@@ -53,10 +53,12 @@ class LinkerBlockAllocator {
  private:
   void create_new_page();
   LinkerBlockAllocatorPage* find_page(void* block);
+  void free_all_pages();
 
   size_t block_size_;
   LinkerBlockAllocatorPage* page_list_;
   void* free_block_list_;
+  size_t allocated_;
 
   DISALLOW_COPY_AND_ASSIGN(LinkerBlockAllocator);
 };
@@ -73,7 +75,8 @@ class LinkerBlockAllocator {
  *    with size 513 this allocator will use 516 (520 for lp64) bytes of data
  *    where generalized implementation is going to use 1024 sized blocks.
  *
- * 2. This allocator does not munmap allocated memory, where LinkerMemoryAllocator does.
+ * 2. Unless all allocated memory is freed, this allocator does not munmap
+ *    allocated memory, where LinkerMemoryAllocator does.
  *
  * 3. This allocator provides mprotect services to the user, where LinkerMemoryAllocator
  *    always treats it's memory as READ|WRITE.