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: <6f9ff0aa-7713-4de1-869e-4725828942e4@arm.com>
Date:   Tue, 28 Nov 2023 23:07:52 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Pasha Tatashin <pasha.tatashin@...een.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 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).

Thanks,
Robin.