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xen-devel
Re: [Xen-devel] [PATCH 3 of 7] docs: add a document describing the xl cf
Tim, George:
Is this broadly accurate? In particular the bit about why one would use
the shadow_memory option and the suggestion that it also controls the
space used by the HAP overhead.
Cheers,
Ian.
On Mon, 2011-11-07 at 15:13 +0000, Ian Campbell wrote:
>
> +### Paging
> +
> +The following options control the mechanisms used to virtualise guest
> +memory. The defaults are selected to give the best results for the
> +common case and so you should normally leave these options
> +unspecified.
> +
> + * `hap=BOOLEAN`: Turns "hardware assisted paging" (the use of the
> + hardware' nested page table feature) on or off. Affects HVM
> guests
> + only. If turned off, Xen will run the guest in "shadow page
> table"
> + mode where the guest's page table updates and/or TLB flushes
> + etc. will be emulated. Use of HAP is the default when available.
> +
> + * `oos=BOOLEAN`: Turns "out of sync pagetables" on or off. When
> + running in shadow page table mode, the guest's page table updates
> + may be deferred as specified in the Intel/AMD architecture
> manuals.
> + However this may expose unexpected bugs in the guest, or find bugs
> + in Xen, so it is possible to disable this feature. Use of out of
> + sync page tables, when Xen thinks it appropriate, is the default.
> +
> + * `shadow_memory=MBYTES`: Number of megabytes to set aside for
> + shadowing guest pagetable pages (effectively acting as a cache of
> + translated pages) or to use for HAP state. By default this is 1MB
> + per guest vcpu plus 8KB per MB of guest RAM. You should not
> + normally need to adjust this value. However if you are not using
> + hardware assisted paging (i.e. you are using shadow mode) and your
> + guest workload consists of a large number of processes which do
> not
> + share address space then increasing this value may improve
> + performance.
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