On Tue, Feb 2, 2021 at 5:39 PM Minchan Kim <minchan@xxxxxxxxxx> wrote: > > On Tue, Feb 02, 2021 at 04:31:34PM -0800, 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] 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@xxxxxxxxxx> > > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > Reviewed-by: Minchan Kim <minchan@xxxxxxxxxx> > > 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.
