On Monday 28 April 2014 03:06 PM, Kirill A. Shutemov wrote:
> 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 <ma...@linux.vnet.ibm.com>
>> ---
>> 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.
>
Ok.
>> 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.
>
Agreed. Will change it.
>> }
>> #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.
>
Sure. Will modify it.
Thanks for review
with regards
Maddy
>> pte = pte_offset_map_lock(mm, pmd, address, &ptl);
>> do_fault_around(vma, address, pte, pgoff, flags);
>> if (!pte_same(*pte, orig_pte))
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