On Mon, Jul 24, 2017 at 01:15:31PM +0200, Jan Kara wrote:
On Sat 22-07-17 09:21:31, Dan Williams wrote:
On Fri, Jul 21, 2017 at 3:39 PM, Ross Zwisler ross.zwisler@linux.intel.com wrote:
To be able to use the common 4k zero page in DAX we need to have our PTE 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 storageThis 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 insert_pfn() 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@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 --- a/drivers/dax/device.c +++ b/drivers/dax/device.c @@ -273,7 +273,7 @@ static int __dev_dax_pte_fault(struct dev_dax *dev_dax, struct vm_fault *vmf)
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 like:
enum { PTE_MKDIRTY, PTE_MKCLEAN, };
...to differentiate the two cases?
So how I usually deal with this is that I create e.g.:
__vm_insert_mixed() that takes the bool argument, make vm_insert_mixed() pass false, and vm_insert_mixed_mkwrite() pass true. That way there's no code duplication, old call sites can stay unchanged, the naming clearly says what's going on...
Ah, that does seem cleaner. I'll try that for v5.