diff options
| -rw-r--r-- | mm/memory.c | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/mm/memory.c b/mm/memory.c index 62a08a7badc4..d67fd9fcf1f2 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2760,6 +2760,10 @@ void do_set_pte(struct vm_area_struct *vma, unsigned long address, static unsigned long fault_around_bytes = 65536; +/* + * fault_around_pages() and fault_around_mask() round down fault_around_bytes + * to nearest page order. It's what do_fault_around() expects to see. + */ static inline unsigned long fault_around_pages(void) { return rounddown_pow_of_two(fault_around_bytes) / PAGE_SIZE; @@ -2801,6 +2805,29 @@ static int __init fault_around_debugfs(void) late_initcall(fault_around_debugfs); #endif +/* + * do_fault_around() tries to map few pages around the fault address. The hope + * is that the pages will be needed soon and this will lower the number of + * faults to handle. + * + * It uses vm_ops->map_pages() to map the pages, which skips the page if it's + * not ready to be mapped: not up-to-date, locked, etc. + * + * This function is called with the page table lock taken. In the split ptlock + * case the page table lock only protects only those entries which belong to + * the page table corresponding to the fault address. + * + * This function doesn't cross the VMA boundaries, in order to call map_pages() + * only once. + * + * fault_around_pages() defines how many pages we'll try to map. + * do_fault_around() expects it to return a power of two less than or equal to + * PTRS_PER_PTE. + * + * The virtual address of the area that we map is naturally aligned to the + * fault_around_pages() value (and therefore to page order). This way it's + * easier to guarantee that we don't cross page table boundaries. + */ static void do_fault_around(struct vm_area_struct *vma, unsigned long address, pte_t *pte, pgoff_t pgoff, unsigned int flags) { |