On Fri, Jul 21, 2017 at 3:39 PM, Ross Zwisler
To be able to use the common 4k zero page in DAX we need to have our
fault path look more like our PMD fault path where a PTE entry can be
marked as dirty and writeable as it is first inserted, rather than waiting
for a follow-up dax_pfn_mkwrite() => finish_mkwrite_fault() call.
Right now we can rely on having a dax_pfn_mkwrite() call because we can
distinguish between these two cases in do_wp_page():
case 1: 4k zero page => writable DAX storage
case 2: read-only DAX storage => writeable DAX storage
This distinction is made by via vm_normal_page(). vm_normal_page() returns
false for the common 4k zero page, though, just as it does for DAX ptes.
Instead of special casing the DAX + 4k zero page case, we will simplify our
DAX PTE page fault sequence so that it matches our DAX PMD sequence, and
get rid of the dax_pfn_mkwrite() helper. We will instead use
dax_iomap_fault() to handle write-protection faults.
This means that insert_pfn() needs to follow the lead of insert_pfn_pmd()
and allow us to pass in a 'mkwrite' flag. If 'mkwrite' is set
will do the work that was previously done by wp_page_reuse() as part of the
dax_pfn_mkwrite() call path.
Signed-off-by: Ross Zwisler <ross.zwisler(a)linux.intel.com>
drivers/dax/device.c | 2 +-
drivers/gpu/drm/exynos/exynos_drm_gem.c | 3 ++-
drivers/gpu/drm/gma500/framebuffer.c | 2 +-
drivers/gpu/drm/msm/msm_gem.c | 3 ++-
drivers/gpu/drm/omapdrm/omap_gem.c | 6 ++++--
drivers/gpu/drm/ttm/ttm_bo_vm.c | 2 +-
fs/dax.c | 2 +-
include/linux/mm.h | 2 +-
mm/memory.c | 27 +++++++++++++++++++++------
9 files changed, 34 insertions(+), 15 deletions(-)
diff --git a/drivers/dax/device.c b/drivers/dax/device.c
index e9f3b3e..3973521 100644
@@ -273,7 +273,7 @@ static int __dev_dax_pte_fault(struct dev_dax *dev_dax, struct
pfn = phys_to_pfn_t(phys, dax_region->pfn_flags);
- rc = vm_insert_mixed(vmf->vma, vmf->address, pfn);
+ rc = vm_insert_mixed(vmf->vma, vmf->address, pfn, false);
Ugh, I generally find bool flags unreadable. They place a tax on
jumping to function definition to recall what true and false mean. If
we want to go this 'add an argument' route can we at least add an enum
...to differentiate the two cases?