[PATCH] MdePkg: Code optimization to SMM InternalAllocateAlignedPages

["duntan" <dun.tan@intel.com>]

This commit is code optimization to InternalAllocateAlignedPages of
SmmMemoryAllocationLib which can reduce free memory fragments. Also
it can reduce one pre-allocation page.

Let's take a simple example:
The expected pages size is 8KB, Alignment value is 8KB.

In original InternalAllocateAlignedPages(), the first step is to
allocate 4 pages and then find the first 8KB-aligned address in the
allocated 4 pages. If the limit address is already 8KB aligned, then
the allocated 4 pages contains two 8KB-aligned 8KB ranges. The lower
2 pages will be selected and removed from free pages. Then the higher
2 pages will be free. Since the whole memory allocation is from high
address to lower address, then the higher 2 pages cann't be merged
other free pages, causing the free memory fragments.

However, when only allocate 3(2+2-1) pages, we can avoid the free
memory fragments in specific case. Also 3 pages must contain a
8kb-aligned 8kb range, which meets the requirement. If the limit
of allocated 3 pages is 8KB-aligned, then the last 8K range will
be selected and removed from free pages. The lower 4Kb will be
free and merged with left lower free memory. This can reduce free
memory fragments in smm.

Signed-off-by: Dun Tan <dun.tan@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Zhiguang Liu <zhiguang.liu@intel.com>
---
 MdePkg/Library/SmmMemoryAllocationLib/MemoryAllocationLib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/MdePkg/Library/SmmMemoryAllocationLib/MemoryAllocationLib.c b/MdePkg/Library/SmmMemoryAllocationLib/MemoryAllocationLib.c
index 3ab2c1ebfd..99a8259325 100644
--- a/MdePkg/Library/SmmMemoryAllocationLib/MemoryAllocationLib.c
+++ b/MdePkg/Library/SmmMemoryAllocationLib/MemoryAllocationLib.c
@@ -322,7 +322,7 @@ InternalAllocateAlignedPages (
     // Calculate the total number of pages since alignment is larger than page size.
     //
     AlignmentMask = Alignment - 1;
-    RealPages     = Pages + EFI_SIZE_TO_PAGES (Alignment);
+    RealPages     = Pages + EFI_SIZE_TO_PAGES (Alignment) - 1;
     //
     // Make sure that Pages plus EFI_SIZE_TO_PAGES (Alignment) does not overflow.
     //
-- 
2.31.1.windows.1