linux-kernel - Re: [PATCH 08/16] iommu/fsl: use page allocation function provided by iommu-pages.h

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Message-ID: <CA+CK2bCOtwZxTUS60PHOQ3szXdCzau7OpopgFEbbC6a9Frxafg@mail.gmail.com>
Date:   Tue, 28 Nov 2023 18:00:13 -0500
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     Robin Murphy <robin.murphy@....com>
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Subject: Re: [PATCH 08/16] iommu/fsl: use page allocation function provided by iommu-pages.h

On Tue, Nov 28, 2023 at 5:53 PM Robin Murphy <robin.murphy@....com> wrote:
>
> On 2023-11-28 8:49 pm, Pasha Tatashin wrote:
> > Convert iommu/fsl_pamu.c to use the new page allocation functions
> > provided in iommu-pages.h.
>
> Again, this is not a pagetable. This thing doesn't even *have* pagetables.
>
> Similar to patches #1 and #2 where you're lumping in configuration
> tables which belong to the IOMMU driver itself, as opposed to pagetables
> which effectively belong to an IOMMU domain's user. But then there are
> still drivers where you're *not* accounting similar configuration
> structures, so I really struggle to see how this metric is useful when
> it's so completely inconsistent in what it's counting :/

The whole IOMMU subsystem allocates a significant amount of kernel
locked memory that we want to at least observe. The new field in
vmstat does just that: it reports ALL buddy allocator memory that
IOMMU allocates. However, for accounting purposes, I agree, we need to
do better, and separate at least iommu pagetables from the rest.

We can separate the metric into two:
iommu pagetable only
iommu everything

or into three:
iommu pagetable only
iommu dma
iommu everything

What do you think?

Pasha

>
> Thanks,
> Robin.
>
> > Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> > ---
> >   drivers/iommu/fsl_pamu.c | 5 +++--
> >   1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/iommu/fsl_pamu.c b/drivers/iommu/fsl_pamu.c
> > index f37d3b044131..7bfb49940f0c 100644
> > --- a/drivers/iommu/fsl_pamu.c
> > +++ b/drivers/iommu/fsl_pamu.c
> > @@ -16,6 +16,7 @@
> >   #include <linux/platform_device.h>
> >
> >   #include <asm/mpc85xx.h>
> > +#include "iommu-pages.h"
> >
> >   /* define indexes for each operation mapping scenario */
> >   #define OMI_QMAN        0x00
> > @@ -828,7 +829,7 @@ static int fsl_pamu_probe(struct platform_device *pdev)
> >               (PAGE_SIZE << get_order(OMT_SIZE));
> >       order = get_order(mem_size);
> >
> > -     p = alloc_pages(GFP_KERNEL | __GFP_ZERO, order);
> > +     p = __iommu_alloc_pages(GFP_KERNEL, order);
> >       if (!p) {
> >               dev_err(dev, "unable to allocate PAACT/SPAACT/OMT block\n");
> >               ret = -ENOMEM;
> > @@ -916,7 +917,7 @@ static int fsl_pamu_probe(struct platform_device *pdev)
> >               iounmap(guts_regs);
> >
> >       if (ppaact)
> > -             free_pages((unsigned long)ppaact, order);
> > +             iommu_free_pages(ppaact, order);
> >
> >       ppaact = NULL;
> >