linux-kernel - Re: [PATCH v2 10/10] iommu: account IOMMU allocated memory

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Message-ID: <CA+CK2bD0Wz8mzB_BGKEYKCHRJKKVwr0CPK7OOC0tD_Sxi5Rp5g@mail.gmail.com>
Date: Fri, 15 Dec 2023 16:11:18 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: David Rientjes <rientjes@...gle.com>
Cc: akpm@...ux-foundation.org, alim.akhtar@...sung.com, alyssa@...enzweig.io, 
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Subject: Re: [PATCH v2 10/10] iommu: account IOMMU allocated memory

> > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> > index 3f85254f3cef..e004e05a7cde 100644
> > --- a/Documentation/admin-guide/cgroup-v2.rst
> > +++ b/Documentation/admin-guide/cgroup-v2.rst
> > @@ -1418,7 +1418,7 @@ PAGE_SIZE multiple when read back.
> >         sec_pagetables
> >               Amount of memory allocated for secondary page tables,
> >               this currently includes KVM mmu allocations on x86
> > -             and arm64.
> > +             and arm64 and IOMMU page tables.
>
> Hmm, if existing users are parsing this field and alerting when it exceeds
> an expected value (a cloud provider, let's say), is it safe to add in a
> whole new set of page tables?
>
> I understand the documentation allows for it, but I think potential impact
> on userspace would be more interesting.

Hi David,

This is something that was discussed at LPC'23. I also was proposing a
separate counter for iommu page tables, but it was noted that we
specifically have sec_pagetables called this way to include all non
regular CPU page tables, and we should therefore account for them
together.

Please also see this discussion from the previous version of this patch series:
https://lore.kernel.org/all/CAJD7tkb1FqTqwONrp2nphBDkEamQtPCOFm0208H3tp0Gq2OLMQ@mail.gmail.com/

Pasha