Re: [PATCH v2] iommu/dma: Use NUMA aware memory allocations in __iommu_dma_alloc_pages()

[John Garry]

On 20/11/2018 14:20, Robin Murphy wrote:
> On 20/11/2018 13:42, John Garry wrote:
> > From: Ganapatrao Kulkarni <ganapatrao.kulkarni@xxxxxxxxxx>
> >
> > Change function __iommu_dma_alloc_pages() to allocate memory/pages
> > for DMA from respective device NUMA node.
> >
> > Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulkarni@xxxxxxxxxx>
> > [JPG:  Modifed to use kvzalloc() and fixed indentation]
> > Signed-off-by: John Garry <john.garry@xxxxxxxxxx>
> > ---
> > Difference v1->v2:
> > - Add Ganapatrao's tag and change author
> >
> > This patch was originally posted by Ganapatrao in [1].
> >
> > However, after initial review, it was never reposted (due to lack of
> > cycles, I think). In addition, the functionality in its sibling patches
> > were merged through patches, as mentioned in [2]; this also refers to a
> > discussion on device local allocations vs CPU local allocations for DMA
> > pool, and which is better [3].
> >
> > However, as mentioned in [3], dma_alloc_coherent() uses the locality
> > information from the device - as in direct DMA - so this patch is just
> > applying this same policy.
> >
> > [1] https://lore.kernel.org/patchwork/patch/833004/
> > [2] https://lkml.org/lkml/2018/8/22/391
> > [3]
> > https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1692998.html
> >
> >
> > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > index d1b0475..ada00bc 100644
> > --- a/drivers/iommu/dma-iommu.c
> > +++ b/drivers/iommu/dma-iommu.c
> > @@ -449,20 +449,17 @@ static void __iommu_dma_free_pages(struct page
> > **pages, int count)
> >       kvfree(pages);
> >   }
> >   -static struct page **__iommu_dma_alloc_pages(unsigned int count,
> > -        unsigned long order_mask, gfp_t gfp)
> > +static struct page **__iommu_dma_alloc_pages(struct device *dev,
> > +        unsigned int count, unsigned long order_mask, gfp_t gfp)
> >   {
> >       struct page **pages;
> > -    unsigned int i = 0, array_size = count * sizeof(*pages);
> > +    unsigned int i = 0, nid = dev_to_node(dev);
> >         order_mask &= (2U << MAX_ORDER) - 1;
> >       if (!order_mask)
> >           return NULL;
> >   -    if (array_size <= PAGE_SIZE)
> > -        pages = kzalloc(array_size, GFP_KERNEL);
> > -    else
> > -        pages = vzalloc(array_size);
> > +    pages = kvzalloc_node(count * sizeof(*pages), GFP_KERNEL, nid);
>
> The pages array is only accessed by the CPU servicing the
> iommu_dma_alloc() call, and is usually freed again before that call even
> returns. It's certainly never touched by the device, so forcing it to a
> potentially non-local node doesn't make a great deal of sense.

Right, it seems sensible to not make this allocation include the 
device-locality requirement, so can leave as is. However modifying to 
use kvzalloc() would seem ok.

> >       if (!pages)
> >           return NULL;
> >   @@ -483,8 +480,10 @@ static struct page
> > **__iommu_dma_alloc_pages(unsigned int count,
> >               unsigned int order = __fls(order_mask);
> >                 order_size = 1U << order;
> > -            page = alloc_pages((order_mask - order_size) ?
> > -                       gfp | __GFP_NORETRY : gfp, order);
> > +            page = alloc_pages_node(nid,
> > +                        (order_mask - order_size) ?
> > +                        gfp | __GFP_NORETRY : gfp,
> > +                        order);
>
> If we're touching this, can we sort out that horrendous ternary? FWIW I
> found I have a local version of the original patch which I tweaked at
> the time, and apparently I reworked this hunk as below, which does seem
> somewhat nicer for the same diffstat.
>
> Robin.
>
>
> @@ -446,10 +443,12 @@ static struct page
> **__iommu_dma_alloc_pages(unsigned int count,
>                 for (order_mask &= (2U << __fls(count)) - 1;
>                      order_mask; order_mask &= ~order_size) {
>                         unsigned int order = __fls(order_mask);
> +                       gfp_t alloc_flags = gfp;
>
>                         order_size = 1U << order;
> -                       page = alloc_pages((order_mask - order_size) ?
> -                                          gfp | __GFP_NORETRY : gfp,
> order);
> +                       if (order_size < order_mask)
> +                               alloc_flags |= __GFP_NORETRY;

Sure, this can be included

> +                       page = alloc_pages_node(nid, alloc_flags, order);
>                         if (!page)
>                                 continue;
>                         if (!order)
>
> .


Cheers,
John