On Thu, Jan 28, 2021 at 12:38:17AM -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. > Clear VM_IO and VM_PFNMAP flags when mapping memory allocated by the > 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 <labb...@kernel.org> > Signed-off-by: Suren Baghdasaryan <sur...@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;
Why do we clear this flag? It shouldn't even be set here as far as I can tell.
