From: Paolo Bonzini <pbonzini@redhat.com>
To: Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel <qemu-devel@nongnu.org>
Cc: Igor Mammedov <imammedo@redhat.com>,
Luiz Capitulino <lcapitulino@redhat.com>
Subject: Re: [Qemu-devel] How guest physical RAM works
Date: Fri, 8 Jan 2016 10:44:25 +0100 [thread overview]
Message-ID: <568F84F9.1050109@redhat.com> (raw)
In-Reply-To: <CAJSP0QUyef1DAmz62XZEokuAdfhRyUcdg9SVfgL1zgh62Zoo3w@mail.gmail.com>
On 08/01/2016 10:29, Stefan Hajnoczi wrote:
> As a side-note, the initial RAM that the guest started with might not
> be modelled with a "pc-dimm" device and it can't be unplugged.
>
> The guest RAM itself isn't contained inside the "pc-dimm" object.
> Instead the "pc-dimm" must be associated with a "memory-backend"
> object.
Perhaps it's worth mentioning that the initial RAM can also be
associated with one or more memory-backend objects, typically one per
virtual NUMA node. The memory-backend is passed to QEMU via "-numa
node,...,memdev=ID".
> The MemoryRegion is the link between guest physical address space and
> the RAMBlocks containing the memory. Each MemoryRegion has the
> ram_addr_t offset of the RAMBlock and each RAMBlock has a MemoryRegion
> pointer.
As a side note (probably beyond the scope of your post) there is no
reason for the MemoryRegion to use the ram_addr_t instead of the
RAMBlock. It would actually be faster if the MemoryRegion contained the
RAMBlock, since it's slow to look up the mmap address corresponding to
the ram_addr_t. There is a 1-element MRU cache, but it's still slowish.
Paolo
prev parent reply other threads:[~2016-01-08 9:44 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-08 9:29 [Qemu-devel] How guest physical RAM works Stefan Hajnoczi
2016-01-08 9:44 ` Paolo Bonzini [this message]
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