Re: memory type information HOB / UEFI memmap defrag

[Jordan Justen <jordan.l.justen@intel.com>]

On 2017-02-21 07:24:11, Laszlo Ersek wrote:
> Hi,
> 
> the UEFI memmap under OVMF is getting very fragmented, I'm now counting
> ~80 entries in it, under various circumstances.
> 
> I recall that a platform's PlatformPei can "prime" the DXE/UEFI memory
> allocation system (not the GCD services) for various memory types, by
> producing a memory type information HOB.
> 
> My vague understanding is that BDS will in turn check if the actual
> allocations fit in the allotments from the HOB, and if not, it will try
> to feed back the increased amount to PEI, for the next boot.
> 
> As far as I understand, this requires the VariablePei (read only driver)
> for a platform (so that its PlatformPei can read the info from BDS, and
> produce the HOB accordingly). Some questions:
> 
> - how big is VariablePei in binary form?
> - does it depend on permanent RAM being installed / discovered?
> - If so, is that dependency implemented with a static DEPEX, or with a
>   callback?
> 
> Further questions:
> - what is the variable (GUID and Name) that BDS uses for this
>   information?

I think grep for EFI_MEMORY_TYPE_INFORMATION_VARIABLE_NAME.

-Jordan

> - What is the format of the variable?
> - Does the logic depend on particular boot modes? OVMF only supports two
>   boot modes, BOOT_WITH_FULL_CONFIGURATION and BOOT_ON_S3_RESUME.
> 
> In OVMF we currently use a static array for populating the HOB (see
> "mDefaultMemoryTypeInformation" in "PlatformPei/Platform.c"). If making
> it all dynamic is easy, I think I'd like to do it (sometime later).
> 
> If, however, it would require us to up-end OVMF's PlatformPei, then I
> think it's not worth it; we can just bump the values in
> "mDefaultMemoryTypeInformation" suitably.
> 
> Some examples I consider as up-ending OVMF's PlatformPei:
> 
> (1) If VariablePei needs permanent RAM with a hard DEPEX. In OVMF,
>     permanent RAM is installed by PlatformPei (thereby potentially
>     unblocking VariablePei's dispatch); however, it is also PlatformPei
>     that would require the r/o variable service to work, because
>     PlatformPei produces the memory type information HOB. So, such a
>     DEPEX in VariablePei would require splitting up PlatformPei, which
>     makes the dynamism totally not worth it.
> 
>     *Maybe* we could add a callback for when the variable service PPI is
>     installed. Dunno.
> 
> (2) Supporting a third boot mode beyond BOOT_WITH_FULL_CONFIGURATION and
>     BOOT_ON_S3_RESUME. Not even worth the audit of current boot mode
>     checks.
> 
> Further remarks:
> 
> - OVMF doesn't care about supporting S4 at the moment, and I personally
>   have no plans to work on that. (I'm saying this because I vaguely
>   recall that the memory type info HOB is related to S4 resume, so an
>   argument could perhaps be made, "this could enable S4 for OVMF".
>   Personally, I'm not interested. Still carrying the scars of S3.)
> 
> - I actually tried to bump the values in "mDefaultMemoryTypeInformation"
>   quite a few months back, but the benefits I saw were negligible. I was
>   left confused about the memory type info HOB, and that was the reason
>   I didn't ultimately post any patch (and why I stopped pursuing this
>   question). For reference, this was the patch:
> 
> > commit b357e8d88c0304ea2b31aefafe53d06c9769fb78
> > Author: Laszlo Ersek <lersek@redhat.com>
> > Date:   Thu Sep 17 16:18:46 2015 +0200
> >
> >     OvmfPkg: PlatformPei: decrease memmap fragmentation
> >
> >     Inspired by ArmVirtPkg commit c199315 ("ArmVirtPkg: increase memory
> >     preallocations to reduce region count"), I checked the number of entries
> >     in the UEFI memory map, as dumped by the UEFI shell's MEMMAP command, and
> >     by the Linux kernel. The number of entries is quite high, about 50-55.
> >
> >     I calculated the new preallocations as follows:
> >     - added 15% to each byte count usage reported by the MEMMAP command, for
> >       some future-proofing,
> >     - expressed the result in kilobytes (both pages and byte counts are hard
> >       to read),
> >     - just for our information, I calculated the ratio between the new
> >       preallocation and the old one.
> >
> >     For example, the UEFI shell reported 44 pages (180224 bytes) of reserved
> >     memory usage. The new preallocation, expressed in kilobytes, is
> >     trunc(180224 * 1.15 / 1024) = 202. This preallocation is approx. 12.62
> >     times the previous preallocation (which was 4 pages, ie. 16384 bytes).
> >
> >     Here's the full table:
> >
> >       memory type  pages from  bytes from  new KB    factor of former
> >                    MEMMAP cmd  MEMMAP cmd  prealloc  prealloc
> >       -----------  ----------  ----------  --------  ----------------
> >       Reserved             44      180224       202             12.62
> >       LoaderCode          313     1282048      1439               n/a
> >       BS_Code            1300     5324800      5980              3.89
> >       BS_Data            9053    37081088     41643              2.71
> >       RT_Code             223      913408      1025              5.33
> >       RT_Data             789     3231744      3629             25.20
> >       ACPI_Recl             8       32768        36              1.12
> >       ACPI_NVS            283     1159168      1301             81.31
> >
> >     ... Unfortunately, when the patch is applied, the memory map remains
> >     fragmented; mostly due to small unused Conventional Memory entries between
> >     other types of allocations. The entry count doesn't go below 40.
> >
> >     Contributed-under: TianoCore Contribution Agreement 1.0
> >     Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> >
> > diff --git a/OvmfPkg/PlatformPei/Platform.c b/OvmfPkg/PlatformPei/Platform.c
> > index a6d961673d3a..38abf3811600 100644
> > --- a/OvmfPkg/PlatformPei/Platform.c
> > +++ b/OvmfPkg/PlatformPei/Platform.c
> > @@ -41,14 +41,15 @@
> >  #include "Cmos.h"
> >
> >  EFI_MEMORY_TYPE_INFORMATION mDefaultMemoryTypeInformation[] = {
> > -  { EfiACPIMemoryNVS,       0x004 },
> > -  { EfiACPIReclaimMemory,   0x008 },
> > -  { EfiReservedMemoryType,  0x004 },
> > -  { EfiRuntimeServicesData, 0x024 },
> > -  { EfiRuntimeServicesCode, 0x030 },
> > -  { EfiBootServicesCode,    0x180 },
> > -  { EfiBootServicesData,    0xF00 },
> > -  { EfiMaxMemoryType,       0x000 }
> > +  { EfiReservedMemoryType,  EFI_SIZE_TO_PAGES ((UINTN)SIZE_1KB *   202) },
> > +  { EfiLoaderCode,          EFI_SIZE_TO_PAGES ((UINTN)SIZE_1KB *  1439) },
> > +  { EfiBootServicesCode,    EFI_SIZE_TO_PAGES ((UINTN)SIZE_1KB *  5980) },
> > +  { EfiBootServicesData,    EFI_SIZE_TO_PAGES ((UINTN)SIZE_1KB * 41643) },
> > +  { EfiRuntimeServicesCode, EFI_SIZE_TO_PAGES ((UINTN)SIZE_1KB *  1025) },
> > +  { EfiRuntimeServicesData, EFI_SIZE_TO_PAGES ((UINTN)SIZE_1KB *  3629) },
> > +  { EfiACPIReclaimMemory,   EFI_SIZE_TO_PAGES ((UINTN)SIZE_1KB *    36) },
> > +  { EfiACPIMemoryNVS,       EFI_SIZE_TO_PAGES ((UINTN)SIZE_1KB *  1301) },
> > +  { EfiMaxMemoryType,       0                                           }
> >  };
> >
> >
> 
> As you can see in the commit message, at that time the patch only
> managed to decrease the number of memmap entries from ~55 to ~40, which
> I found "meh". I figured I'd ask again, because now I'm seeing about 80
> entries in the memmap. (I wonder if that is related to OVMF's recently
> increased ACPI S3 boot script usage!)
> 
> Thanks,
> Laszlo
> 
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