linux-kernel - Re: [PATCHv5 06/12] x86/boot/compressed: Handle unaccepted memory

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Message-ID: <0e0533ab-cbb4-b8da-66cf-e838d9ed9ea3@amd.com>
Date:   Wed, 1 Jun 2022 23:19:46 +0200
From:   "Gupta, Pankaj" <pankaj.gupta@....com>
To:     Randy Dunlap <rdunlap@...radead.org>,
        Dionna Amalie Glaze <dionnaglaze@...gle.com>
Cc:     "Xu, Min M" <min.m.xu@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>,
        "Gao, Jiaqi" <jiaqi.gao@...el.com>,
        Michael Roth <michael.roth@....com>,
        Borislav Petkov <bp@...en8.de>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Rodel, Jorg" <jroedel@...e.de>, Ard Biesheuvel <ardb@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Varad Gautam <varad.gautam@...e.com>,
        Dario Faggioli <dfaggioli@...e.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv5 06/12] x86/boot/compressed: Handle unaccepted memory


>> The memory accounting in Linux is probably the issue. Both times I ran
>> the test were from a freshly booted VM. The test parses the output of
>> $(free -k) to determine the amount of free memory it should allocate
>> and write/read from, with a given stride of pages to skip before
>> touching the next page.
>>
>> We grab the third column of numbers from the Mem output that looks like this
>>
>>                 total        used        free      shared  buff/cache   available
>> Mem:        65856604     4128688    48558952       11208    13168964    60942928
>> Swap:        1953788      118124     1835664
>>
>> So my workstation has 48558952 free bytes. We take that, give it to
>> memtouch to allocate that much anonymous memory rounded down to the
>> nearest MB with mmap and randomly read/write the buffer.
>>
>> For an 8GB machine, the UEFI will have the initial 0-0xA000 memory and
>> 0x10_0000 to 0xC00_0000 (beginning of mmio hole) prevalidated. The
>> next 5GB is classified as the UEFI v2.9 memory type
>> EFI_RESOURCE_MEMORY_UNACCEPTED, 0x1_4000_000 to 0x2_0000_0000.
>> The Linux e820 map should see that range as unaccepted rather than
>> EFI_CONVENTIONAL_MEMORY (i.e., EDK2's EFI_RESOURCE_SYSTEM_MEMORY), but
>> I think it needs to be accounted as free conventional memory.
>>
>> So when I see 2044MB free vs 7089MB free in my VMs, the two are
>> roughly 5GB different.
> 
> Please see/read/use
...

Apologies, some problem in my email client (appending long characters to 
links), will find and correct.

Thank you for pointing.

Best regards,
Pankaj