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Date:   Tue, 2 Feb 2021 18:07:38 -0800
From:   John Stultz <>
To:     Suren Baghdasaryan <>
Cc:     Sumit Semwal <>,
        Andrew Morton <>,
        Christoph Hellwig <>,
        Liam Mark <>,
        Laura Abbott <>,
        Brian Starkey <>,
        Christian Koenig <>,
        Chris Goldsworthy <>,
        Ørjan Eide <>,
        Robin Murphy <>,
        James Jones <>,
        Minchan Kim <>,
        Hridya Valsaraju <>,
        Sandeep Patil <>,
        linux-media <>,
        dri-devel <>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <>, linux-mm <>,
        lkml <>,
        Android Kernel Team <>
Subject: Re: [PATCH v2 2/2] dma-buf: heaps: Map system heap pages as managed
 by linux vm

On Tue, Feb 2, 2021 at 4:31 PM Suren Baghdasaryan <> 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.
> Replace remap_pfn_range with vm_insert_page, following Laura's suggestion
> in [1]. This would allow correct PSS calculation for dmabufs.
> [1]
> [2]
> (sorry, could not find lore links for these discussions)
> Suggested-by: Laura Abbott <>
> Signed-off-by: Suren Baghdasaryan <>

For consistency, do we need something similar for the cma heap as well?


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