[Patch V2] 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
allocated 4 pages. If the upper limit address of allocated 4 pages
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 low
address, then the higher 2 pages cann't be merged with 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 upper
limit address of allocated 3 pages is 8KB-aligned, then the higher
2 pages range of allocated 3 pages is 8KB-aligned and will be
selected and removed from free pages. The remaining lower one page
of allocated 3 pages 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