linux-kernel - Re: [PATCH 05/16] iommu/io-pgtable-arm-v7s: use page allocation function provided by iommu-pages.h

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Message-ID: <CA+CK2bDKaXqemr2Hp=MRxxMB_=AoRnUK_D2SGm9cDkKa+JaT7A@mail.gmail.com>
Date:   Tue, 28 Nov 2023 18:32:20 -0500
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     Robin Murphy <robin.murphy@....com>
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Subject: Re: [PATCH 05/16] iommu/io-pgtable-arm-v7s: use page allocation
 function provided by iommu-pages.h

On Tue, Nov 28, 2023 at 6:08 PM Robin Murphy <robin.murphy@....com> wrote:
>
> On 2023-11-28 10:55 pm, Pasha Tatashin wrote:
> >>>                kmem_cache_free(data->l2_tables, table);
> >
> > We only account page allocations, not subpages, however, this is
> > something I was surprised about this particular architecture of why do
> > we allocate l2 using kmem ? Are the second level tables on arm v7s
> > really sub-page in size?
>
> Yes, L2 tables are 1KB, so the kmem_cache could still quite easily end
> up consuming significantly more memory than the L1 table, which is
> usually 16KB (but could potentially be smaller depending on the config,
> or up to 64KB with the Mediatek hacks).

I am OK removing support for this architecture, or keeping only info
for L1, I do not think there is a reason to worry about sub-page
accounting only for v7s.

Pasha

>
> Thanks,
> Robin.