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RE: [PATCH for-4.17 1/2] docs: Document the minimal requirement of static heap
- To: Julien Grall <julien@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Henry Wang <Henry.Wang@xxxxxxx>
- Date: Fri, 14 Oct 2022 08:58:14 +0000
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Wei Chen <Wei.Chen@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Fri, 14 Oct 2022 08:58:34 +0000
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- Thread-topic: [PATCH for-4.17 1/2] docs: Document the minimal requirement of static heap
Hi Julien,
> -----Original Message-----
> From: Julien Grall <julien@xxxxxxx>
> Subject: Re: [PATCH for-4.17 1/2] docs: Document the minimal requirement
> of static heap
>
> Hi Henry,
>
> > +Users should be mindful that the static heap should at least satisfy the
> > +allocation of the P2M maps for all guests. Currently, the minimal
> requirement
> > +of per-domain P2M pages pool is in-sync with function
> > +libxl__get_required_paging_memory() (for xl-created domUs) and
> > +domain_p2m_pages() (for dom0less domUs), that is, 1MB per vCPU, plus
> 4KiB per
> > +MiB of RAM for the P2M map, and plus 512KiB to cover extended regions.
>
> I think this wording is OK if the feature is a tech preview. However, if
> this is security supported, we need to provide some more details about
> the size.
>
> In particular, this doesn't tell a user how they can find the size that
> would fit them. Can this be decided with a formula?
My feeling of the formula would be:
My feeling of the formula would be:
Total heap size needed per guest = 1MB * num_guest_vcpu +
4KB * guest_ram_size_in_mb + 512KB +
the memory allocated from heap by xzalloc/xzalloc_array for various uses
for example alloc_domain_struct(), d->shared_info, evtchn_bucket, etc.
Is this formula somehow make sense to you? I think we need to have a
rough estimation of the last part (boot time allocation) though.
Kind regards,
Henry
>
> If not, could a user configure his system without the reserved heap and
> find out the memory usage from dom0 (or a debug keys)?
>
> Cheers,
>
>
> --
> Julien Grall
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