Re: memory type information HOB / UEFI memmap defrag

[Laszlo Ersek <lersek@redhat.com>]

On 02/21/17 23:35, Jordan Justen wrote:
> 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.

Thanks, that looks very interesting:

* Apparently, if the PEI phase does not produce the info HOB, but it
includes the VariablePei driver, then the DXE IPL PEIM will itself build
the HOB, from the variable.

This seems to eliminate a lot of trouble: for example, if the platform
includes VariablePei, then that will surely be available by the time the
DXE IPL PEIM looks for it, in DxeLoadCore(). (No ordering or dependency
problems, that is!)

* BmSetMemoryTypeInformationVariable()
[MdeModulePkg/Library/UefiBootManagerLib/BmMisc.c] seems to read the
variable (if it exists) under all boot modes different from
BOOT_WITH_DEFAULT_SETTINGS, and to set the variable if it doesn't exist,
or the page counts were changed.

For BOOT_WITH_FULL_CONFIGURATION, as a special case of the above, the
page counts never decrease, only increase, which looks good too.


Based on the above, solving the fragmentation could be as simple as: (a)
including VariablePei in OvmfPkg, (b) removing the HOB production from
OvmfPkg/PlatformPei.

I'll give it a whirl later on, and see how it affects the fragmentation.

Thank you Jordan, this was *really* helpful!
Laszlo

> 
> -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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