[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH] q35: split memory at 2G
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] q35: split memory at 2G |
Date: |
Wed, 29 May 2019 03:21:16 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 |
On 28/05/19 22:48, Gerd Hoffmann wrote:
> Original q35 behavior was to split memory 2.75 GB, leaving space for the
> mmconfig bar at 0xb000000 and pci I/O window starting at 0xc0000000.
>
> Note: Those machine types have been removed from the qemu codebase
> meanwhile because they could not be live-migrated so there was little
> value in keeping them around.
>
> With the effort to allow for gigabyte-alignment of guest memory that
> behavior was changed: The split was moved to 2G, but only in case the
> memory didn't fit below 2.75 GB.
>
> So today the address space between 2G and 2,75G is not used for guest
> memory in typical use cases, where the guest memory sized at a power of
> two or a gigabyte number. But if you configure your guest with some odd
> amout of memory (such as 2.5G) the address space is used.
Wasn't it done to ensure pre-PAE OSes could use as much memory as
possible? (If you run pre-PAE OSes with more RAM than can fit below 4G,
you can just reduce the amount of memory and get all the 2.75G).
Paolo