linux-kernel - Re: [PATCH v3 00/10] IOMMU memory observability

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Message-ID: <CA+CK2bCUGepLLA2Hsmq00XEhPzLWPb5CjzY_UPT0qWSKastjAQ@mail.gmail.com>
Date: Thu, 4 Jan 2024 14:12:26 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Michal Koutný <mkoutny@...e.com>
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Subject: Re: [PATCH v3 00/10] IOMMU memory observability

On Thu, Jan 4, 2024 at 12:04 PM Michal Koutný <mkoutny@...e.com> wrote:
>
> On Thu, Jan 04, 2024 at 11:29:43AM -0500, Pasha Tatashin <pasha.tatashin@...een.com> wrote:
> > Thank you for taking a look at this. The two patches [1] [2] which add
> > GFP_KERNEL_ACCOUNT were sent separate from this series at request of
> > reviewers:
>
> Ah, I didn't catch that.
>
> Though, I mean the patch 02/10 calls iommu_alloc_pages() with GFP_KERNEL
> (and not a passed gfp from iommu_map).
> Then patch 09/10 accounts all iommu_alloc_pages() under NR_IOMMU_PAGES.
>
> I think there is a difference between what's shown NR_IOMMU_PAGES and
> what will have __GFP_ACCOUNT because of that.
>
> I.e. is it the intention that this difference is not subject to
> limiting?

Yes, we will have a difference between GFP_ACCOUNT and what
NR_IOMMU_PAGES shows. GFP_ACCOUNT is set only where it makes sense to
charge to user processes, i.e. IOMMU Page Tables, but there more IOMMU
shared data that should not really be charged to a specific process.
The charged and uncharged data will be visible via /proc/vmstat
nr_iommu_pages field.

Pasha

>
> (Note: I'm not familiar with iommu code and moreover I'm only looking at
> the two patch sets, not the complete code applied. So you may correct my
> reasoning.)
>
>
> Thanks,
> Michal