From: Pasha Tatashin <pasha.tatashin@soleen.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Will Deacon <will@kernel.org>,
akpm@linux-foundation.org, alim.akhtar@samsung.com,
alyssa@rosenzweig.io, asahi@lists.linux.dev,
baolu.lu@linux.intel.com, bhelgaas@google.com,
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dwmw2@infradead.org, hannes@cmpxchg.org, heiko@sntech.de,
iommu@lists.linux.dev, jernej.skrabec@gmail.com,
jonathanh@nvidia.com, joro@8bytes.org,
krzysztof.kozlowski@linaro.org, linux-doc@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
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paulmck@kernel.org, rdunlap@infradead.org, robin.murphy@arm.com,
samuel@sholland.org, suravee.suthikulpanit@amd.com,
sven@svenpeter.dev, thierry.reding@gmail.com, tj@kernel.org,
tomas.mudrunka@gmail.com, vdumpa@nvidia.com, wens@csie.org,
yu-cheng.yu@intel.com, rientjes@google.com
Subject: Re: [PATCH v3 10/10] iommu: account IOMMU allocated memory
Date: Wed, 21 Feb 2024 19:27:07 -0500 [thread overview]
Message-ID: <CA+CK2bBGzM8Xbfq9A7HHNr40oukvAk7-1RK7AFbW3qFcNstb5g@mail.gmail.com> (raw)
In-Reply-To: <20240222002152.GG13491@ziepe.ca>
> > > > > While I can see the value in this for IOMMU mappings managed by VFIO,
> > > > > doesn't this end up conflating that with the normal case of DMA domains?
> > > > > For systems that e.g. rely on an IOMMU for functional host DMA, it seems
> > > > > wrong to subject that to accounting constraints.
> > > >
> > > > The accounting constraints are only applicable when GFP_KERNEL_ACCOUNT
> > > > is passed to the iommu mapping functions. We do that from the vfio,
> > > > iommufd, and vhost. Without this flag, the memory useage is reported
> > > > in /proc/meminfo as part of SecPageTables field, but not constrained
> > > > in cgroup.
> > >
> > > Thanks, Pasha, that explanation makes sense. I still find it bizarre to
> > > include IOMMU allocations from the DMA API in SecPageTables though, and
> > > I worry that it will confuse people who are using that metric as a way
> > > to get a feeling for how much memory is being used by KVM's secondary
> > > page-tables. As an extreme example, having a non-zero SecPageTables count
> > > without KVM even compiled in is pretty bizarre.
> >
> > I agree; I also prefer a new field in /proc/meminfo named
> > 'IOMMUPageTables'. This is what I proposed at LPC, but I was asked to
> > reuse the existing 'SecPageTables' field instead. The rationale was
> > that 'secondary' implies not only KVM page tables, but any other
> > non-regular page tables.
>
> Right, SeanC mentioned that the purpose of SecPageTables was to
> capture all non-mm page table radix allocations.
>
> > I would appreciate the opinion of IOMMU maintainers on this: is it
> > preferable to bundle the information with 'SecPageTables' or maintain
> > a separate field?
>
> I think you should keep them together. I don't think we should be
> introducing new counters, in general.
Thanks Jason, I will keep it as-is. I will send a new version soon
with your comments addressed.
> Detailed memory profile should come from some kind of more dynamic and
> universal scheme. Hopefully that other giant thread about profiling
> will reach some conclusion.
+1! Memory profiling is going to be a very useful addition to the kernel.
Pasha
next prev parent reply other threads:[~2024-02-22 0:27 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-26 20:01 [PATCH v3 00/10] IOMMU memory observability Pasha Tatashin
2023-12-26 20:01 ` [PATCH v3 01/10] iommu/vt-d: add wrapper functions for page allocations Pasha Tatashin
2023-12-27 0:27 ` David Rientjes
2023-12-26 20:01 ` [PATCH v3 02/10] iommu/amd: use page allocation function provided by iommu-pages.h Pasha Tatashin
2023-12-26 20:01 ` [PATCH v3 03/10] iommu/io-pgtable-arm: " Pasha Tatashin
2023-12-26 20:01 ` [PATCH v3 04/10] iommu/io-pgtable-dart: " Pasha Tatashin
2023-12-26 20:02 ` [PATCH v3 05/10] iommu/exynos: " Pasha Tatashin
2023-12-26 20:02 ` [PATCH v3 06/10] iommu/rockchip: " Pasha Tatashin
2023-12-26 20:02 ` [PATCH v3 07/10] iommu/sun50i: " Pasha Tatashin
2023-12-26 20:02 ` [PATCH v3 08/10] iommu/tegra-smmu: " Pasha Tatashin
2024-01-05 8:20 ` Thierry Reding
2023-12-26 20:02 ` [PATCH v3 09/10] iommu: observability of the IOMMU allocations Pasha Tatashin
2023-12-26 20:02 ` [PATCH v3 10/10] iommu: account IOMMU allocated memory Pasha Tatashin
2023-12-27 0:25 ` David Rientjes
2024-02-13 13:12 ` Will Deacon
2024-02-13 15:44 ` Pasha Tatashin
2024-02-16 17:57 ` Will Deacon
2024-02-16 19:48 ` Pasha Tatashin
2024-02-21 13:29 ` Will Deacon
2024-02-22 0:21 ` Jason Gunthorpe
2024-02-22 0:27 ` Pasha Tatashin [this message]
2023-12-27 10:05 ` [PATCH v3 00/10] IOMMU memory observability Bagas Sanjaya
2023-12-28 14:36 ` Pasha Tatashin
2024-01-04 15:31 ` Michal Koutný
2024-01-04 16:29 ` Pasha Tatashin
2024-01-04 17:04 ` Michal Koutný
2024-01-04 19:12 ` Pasha Tatashin
2024-01-05 9:02 ` Michal Koutný
2024-01-05 15:33 ` Pasha Tatashin
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