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From:   John Stultz <john.stultz@linaro.org>
Date:   Tue, 2 Feb 2021 18:07:38 -0800
Message-ID: <CALAqxLWJNDDx_MFvYHszFXy=aV9bZGi50L3zDtuGaiYUbHKHSA@mail.gmail.com>
Subject: Re: [PATCH v2 2/2] dma-buf: heaps: Map system heap pages as managed
 by linux vm
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     Sumit Semwal <sumit.semwal@linaro.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Hellwig <hch@infradead.org>,
        Liam Mark <lmark@codeaurora.org>,
        Laura Abbott <labbott@redhat.com>,
        Brian Starkey <Brian.Starkey@arm.com>,
        Christian Koenig <christian.koenig@amd.com>,
        Chris Goldsworthy <cgoldswo@codeaurora.org>,
        =?UTF-8?Q?=C3=98rjan_Eide?= <orjan.eide@arm.com>,
        Robin Murphy <robin.murphy@arm.com>,
        James Jones <jajones@nvidia.com>,
        Minchan Kim <minchan@kernel.org>,
        Hridya Valsaraju <hridya@google.com>,
        Sandeep Patil <sspatil@google.com>,
        linux-media <linux-media@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@lists.linaro.org>, linux-mm <linux-mm@kvack.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Android Kernel Team <kernel-team@android.com>
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On Tue, Feb 2, 2021 at 4:31 PM 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.
> 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>

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

thanks
-john