Re: [PATCH v2 2/2] dma-buf: heaps: Map system heap pages as managed by linux vm
From: Suren Baghdasaryan <surenb@google.com>
Date: 2021-02-03 02:03:25
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dri-devel, linux-mm, lkml
On Tue, Feb 2, 2021 at 5:39 PM Minchan Kim [off-list ref] wrote:
On Tue, Feb 02, 2021 at 04:31:34PM -0800, Suren Baghdasaryan wrote:quoted
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>Reviewed-by: Minchan Kim <minchan@kernel.org> A note: This patch makes dmabuf system heap accounted as PSS so if someone has relies on the size, they will see the bloat. IIRC, there was some debate whether PSS accounting for their buffer is correct or not. If it'd be a problem, we need to discuss how to solve it(maybe, vma->vm_flags and reintroduce remap_pfn_range for them to be respected).
I did not see debates about not including *mapped* dmabufs into PSS calculation. I remember people were discussing how to account dmabufs referred only by the FD but that is a different discussion. If the buffer is mapped into the address space of a process then IMHO including it into PSS of that process is not controversial.