Madhavan Srinivasan wrote:
> Kirill A. Shutemov with 8c6e50b029 commit introduced
> vm_ops->map_pages() for mapping easy accessible pages around
> fault address in hope to reduce number of minor page faults.
>
> This patch creates infrastructure to modify the FAULT_AROUND_ORDER
> value using mm/Kconfig. This will enable architecture maintainers
> to decide on suitable FAULT_AROUND_ORDER value based on
> performance data for that architecture. Patch also defaults
> FAULT_AROUND_ORDER Kconfig element to 4.
>
> Signed-off-by: Madhavan Srinivasan <maddy@xxxxxxxxxxxxxxxxxx>
> ---
> mm/Kconfig | 8 ++++++++
> mm/memory.c | 11 ++++-------
> 2 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index ebe5880..c7fc4f1 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -176,6 +176,14 @@ config MOVABLE_NODE
> config HAVE_BOOTMEM_INFO_NODE
> def_bool n
>
> +#
> +# Fault around order is a control knob to decide the fault around pages.
> +# Default value is set to 4 , but the arch can override it as desired.
> +#
> +config FAULT_AROUND_ORDER
> + int
> + default 4
> +
> # eventually, we can have this option just 'select SPARSEMEM'
> config MEMORY_HOTPLUG
> bool "Allow for memory hot-add"
> diff --git a/mm/memory.c b/mm/memory.c
> index d0f0bef..457436d 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3382,11 +3382,9 @@ void do_set_pte(struct vm_area_struct *vma, unsigned long address,
> update_mmu_cache(vma, address, pte);
> }
>
> -#define FAULT_AROUND_ORDER 4
> +unsigned int fault_around_order = CONFIG_FAULT_AROUND_ORDER;
>
> #ifdef CONFIG_DEBUG_FS
> -static unsigned int fault_around_order = FAULT_AROUND_ORDER;
> -
> static int fault_around_order_get(void *data, u64 *val)
> {
> *val = fault_around_order;
> @@ -3395,7 +3393,6 @@ static int fault_around_order_get(void *data, u64 *val)
>
> static int fault_around_order_set(void *data, u64 val)
> {
> - BUILD_BUG_ON((1UL << FAULT_AROUND_ORDER) > PTRS_PER_PTE);
> if (1UL << val > PTRS_PER_PTE)
> return -EINVAL;
> fault_around_order = val;
> @@ -3430,14 +3427,14 @@ static inline unsigned long fault_around_pages(void)
> {
> unsigned long nr_pages;
>
> - nr_pages = 1UL << FAULT_AROUND_ORDER;
> + nr_pages = 1UL << fault_around_order;
> BUILD_BUG_ON(nr_pages > PTRS_PER_PTE);
This BUILD_BUG_ON() doesn't make sense any more since compiler usually can't
prove anything about extern variable.
Drop it or change to VM_BUG_ON() or something.
> return nr_pages;
> }
>
> static inline unsigned long fault_around_mask(void)
> {
> - return ~((1UL << (PAGE_SHIFT + FAULT_AROUND_ORDER)) - 1);
> + return ~((1UL << (PAGE_SHIFT + fault_around_order)) - 1);
fault_around_pages() and fault_around_mask() should be moved outside of
#ifdef CONFIG_DEBUG_FS and consolidated since they are practically identical
both branches after the changes.
> }
> #endif
>
> @@ -3495,7 +3492,7 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> * if page by the offset is not ready to be mapped (cold cache or
> * something).
> */
> - if (vma->vm_ops->map_pages) {
> + if ((vma->vm_ops->map_pages) && (fault_around_order)) {
Way too many parentheses.
> pte = pte_offset_map_lock(mm, pmd, address, &ptl);
> do_fault_around(vma, address, pte, pgoff, flags);
> if (!pte_same(*pte, orig_pte))
--
Kirill A. Shutemov
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