Re: [edk2-devel] [Patch V2] MdePkg: Code optimization to SMM InternalAllocateAlignedPages

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

Hi Mike and Liming,

Could you please help to review this patch?

Thanks,
Dun

-----Original Message-----
From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of duntan
Sent: Thursday, May 18, 2023 3:31 PM
To: devel@edk2.groups.io
Cc: Ni, Ray <ray.ni@intel.com>; Kinney, Michael D <michael.d.kinney@intel.com>; Gao, Liming <gaoliming@byosoft.com.cn>; Liu, Zhiguang <zhiguang.liu@intel.com>
Subject: [edk2-devel] [Patch V2] MdePkg: Code optimization to SMM InternalAllocateAlignedPages

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