Re: [PATCH 1/1] dma-buf: heaps: Map system heap pages as managed by linux vm

[Suren Baghdasaryan <surenb@google.com>]

On Thu, Jan 28, 2021 at 12:38 AM Suren Baghdasaryan <surenb@google.com> wrote:
>
> Currently system heap maps its buffers with VM_PFNMAP flag using
> remap_pfn_range. This results in such buffers not being accounted
> for in PSS calculations because vm treats this memory as having no
> page structs. Without page structs there are no counters representing
> how many processes are mapping a page and therefore PSS calculation
> is impossible.
> Historically, ION driver used to map its buffers as VM_PFNMAP areas
> due to memory carveouts that did not have page structs [1]. That
> is not the case anymore and it seems there was desire to move away
> from remap_pfn_range [2].
> Dmabuf system heap design inherits this ION behavior and maps its
> pages using remap_pfn_range even though allocated pages are backed
> by page structs.
> Clear VM_IO and VM_PFNMAP flags when mapping memory allocated by the

Agrh, please ignore VM_IO in the description. The patch does not touch
that flag. I'll fix that in the next revision.

> system heap and replace remap_pfn_range with vm_insert_page, following
> Laura's suggestion in [1]. This would allow correct PSS calculation
> for dmabufs.
>
> [1] https://driverdev-devel.linuxdriverproject.narkive.com/v0fJGpaD/using-ion-memory-for-direct-io
> [2] http://driverdev.linuxdriverproject.org/pipermail/driverdev-devel/2018-October/127519.html
> (sorry, could not find lore links for these discussions)
>
> Suggested-by: Laura Abbott <labbott@kernel.org>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
>  drivers/dma-buf/heaps/system_heap.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
> index 17e0e9a68baf..0e92e42b2251 100644
> --- a/drivers/dma-buf/heaps/system_heap.c
> +++ b/drivers/dma-buf/heaps/system_heap.c
> @@ -200,11 +200,13 @@ static int system_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
>         struct sg_page_iter piter;
>         int ret;
>
> +       /* All pages are backed by a "struct page" */
> +       vma->vm_flags &= ~VM_PFNMAP;
> +
>         for_each_sgtable_page(table, &piter, vma->vm_pgoff) {
>                 struct page *page = sg_page_iter_page(&piter);
>
> -               ret = remap_pfn_range(vma, addr, page_to_pfn(page), PAGE_SIZE,
> -                                     vma->vm_page_prot);
> +               ret = vm_insert_page(vma, addr, page);
>                 if (ret)
>                         return ret;
>                 addr += PAGE_SIZE;
> --
> 2.30.0.280.ga3ce27912f-goog
>