linux-kernel - Re: [PATCH v2 01/10] iommu/vt-d: add wrapper functions for page allocations

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Message-ID: <1fd66377-030c-2e48-e658-4669bbf037e9@google.com>
Date: Sun, 24 Dec 2023 13:30:50 -0800 (PST)
From: David Rientjes <rientjes@...gle.com>
To: Pasha Tatashin <pasha.tatashin@...een.com>
cc: Andrew Morton <akpm@...ux-foundation.org>, alim.akhtar@...sung.com, 
    alyssa@...enzweig.io, asahi@...ts.linux.dev, baolu.lu@...ux.intel.com, 
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Subject: Re: [PATCH v2 01/10] iommu/vt-d: add wrapper functions for page
 allocations

On Thu, 14 Dec 2023, Pasha Tatashin wrote:

> On Thu, Dec 14, 2023 at 12:58 PM David Rientjes <rientjes@...gle.com> wrote:
> >
> > On Thu, 30 Nov 2023, Pasha Tatashin wrote:
> >
> > > diff --git a/drivers/iommu/iommu-pages.h b/drivers/iommu/iommu-pages.h
> > > new file mode 100644
> > > index 000000000000..2332f807d514
> > > --- /dev/null
> > > +++ b/drivers/iommu/iommu-pages.h
> > > @@ -0,0 +1,199 @@
> > > +/* SPDX-License-Identifier: GPL-2.0-only */
> > > +/*
> > > + * Copyright (c) 2023, Google LLC.
> > > + * Pasha Tatashin <pasha.tatashin@...een.com>
> > > + */
> > > +
> > > +#ifndef __IOMMU_PAGES_H
> > > +#define __IOMMU_PAGES_H
> > > +
> > > +#include <linux/vmstat.h>
> > > +#include <linux/gfp.h>
> > > +#include <linux/mm.h>
> > > +
> > > +/*
> > > + * All page allocation that are performed in the IOMMU subsystem must use one of
> > > + * the functions below.  This is necessary for the proper accounting as IOMMU
> > > + * state can be rather large, i.e. multiple gigabytes in size.
> > > + */
> > > +
> > > +/**
> > > + * __iommu_alloc_pages_node - allocate a zeroed page of a given order from
> > > + * specific NUMA node.
> > > + * @nid: memory NUMA node id
> >
> > NUMA_NO_NODE if no locality requirements?
> 
> If no locality is required, there is a better interface:
> __iommu_alloc_pages(). That one will also take a look at the calling
> process policies to determine the proper NUMA node when nothing is
> specified. However, when policies should be ignored, and no locality
> required, NUMA_NO_NODE can be passed.
> 

Gotcha, thanks!

> >
> > > + * @gfp: buddy allocator flags
> > > + * @order: page order
> > > + *
> > > + * returns the head struct page of the allocated page.
> > > + */
> > > +static inline struct page *__iommu_alloc_pages_node(int nid, gfp_t gfp,
> > > +                                                 int order)
> > > +{
> > > +     struct page *pages;
> >
> > s/pages/page/ here and later in this file.
> 
> In this file, where there a page with an "order", I reference it with
> "pages", when no order (i.e. order = 0), I reference it with "page"
> 
> I.e.: __iommu_alloc_page vs. __iommu_alloc_pages
> 

Eh, the struct page points to a (potentially compound) page, not a set or 
list of pages.  I won't bikeshed on it, but "struct page *pages" never 
makes sense unless it's **pages or *pages[] :)