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

["Ni, Ray" <ray.ni@intel.com>]

Reviewed-by: Ray Ni <ray.ni@intel.com>

> -----Original Message-----
> From: Tan, Dun <dun.tan@intel.com>
> 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: [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