Michal Hocko <mhocko@xxxxxxxxxx> writes:
> On Tue 15-05-18 08:57:56, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@xxxxxxxxx>
>>
>> This is to take better advantage of huge page clearing
>> optimization (c79b57e462b5d, "mm: hugetlb: clear target sub-page last
>> when clearing huge page"). Which will clear to access sub-page last
>> to avoid the cache lines of to access sub-page to be evicted when
>> clearing other sub-pages. This needs to get the address of the
>> sub-page to access, that is, the fault address inside of the huge
>> page. So the hugetlb no page fault handler is changed to pass that
>> information. This will benefit workloads which don't access the begin
>> of the huge page after page fault.
>>
>> With this patch, the throughput increases ~28.1% in vm-scalability
>> anon-w-seq test case with 88 processes on a 2 socket Xeon E5 2699 v4
>> system (44 cores, 88 threads). The test case creates 88 processes,
>> each process mmap a big anonymous memory area and writes to it from
>> the end to the begin. For each process, other processes could be seen
>> as other workload which generates heavy cache pressure. At the same
>> time, the cache miss rate reduced from ~36.3% to ~25.6%, the
>> IPC (instruction per cycle) increased from 0.3 to 0.37, and the time
>> spent in user space is reduced ~19.3%
>
> This paragraph is confusing as Mike mentioned already. It would be
> probably more helpful to see how was the test configured to use hugetlb
> pages and what is the end benefit.
Sure. Will revise it.
> I do not have any real objection to the implementation so feel free to
> add
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
> I am just wondering what is the usecase driving this. Or is it just a
> generic optimization that always makes sense to do? Indicating that in
> the changelog would be helpful as well.
I think this is a generic optimization.
Best Regards,
Huang, Ying
> Thanks!
>
>> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
>> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
>> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
>> Cc: Andi Kleen <andi.kleen@xxxxxxxxx>
>> Cc: Jan Kara <jack@xxxxxxx>
>> Cc: Michal Hocko <mhocko@xxxxxxxx>
>> Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
>> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
>> Cc: Minchan Kim <minchan@xxxxxxxxxx>
>> Cc: Shaohua Li <shli@xxxxxx>
>> Cc: Christopher Lameter <cl@xxxxxxxxx>
>> Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
>> Cc: Punit Agrawal <punit.agrawal@xxxxxxx>
>> Cc: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
>> ---
>> mm/hugetlb.c | 12 ++++++------
>> 1 file changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 129088710510..3de6326abf39 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -3677,7 +3677,7 @@ int huge_add_to_page_cache(struct page *page, struct address_space *mapping,
>>
>> static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
>> struct address_space *mapping, pgoff_t idx,
>> - unsigned long address, pte_t *ptep, unsigned int flags)
>> + unsigned long faddress, pte_t *ptep, unsigned int flags)
>> {
>> struct hstate *h = hstate_vma(vma);
>> int ret = VM_FAULT_SIGBUS;
>> @@ -3686,6 +3686,7 @@ static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
>> struct page *page;
>> pte_t new_pte;
>> spinlock_t *ptl;
>> + unsigned long address = faddress & huge_page_mask(h);
>>
>> /*
>> * Currently, we are forced to kill the process in the event the
>> @@ -3749,7 +3750,7 @@ static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
>> ret = VM_FAULT_SIGBUS;
>> goto out;
>> }
>> - clear_huge_page(page, address, pages_per_huge_page(h));
>> + clear_huge_page(page, faddress, pages_per_huge_page(h));
>> __SetPageUptodate(page);
>> set_page_huge_active(page);
>>
>> @@ -3871,7 +3872,7 @@ u32 hugetlb_fault_mutex_hash(struct hstate *h, struct mm_struct *mm,
>> #endif
>>
>> int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>> - unsigned long address, unsigned int flags)
>> + unsigned long faddress, unsigned int flags)
>> {
>> pte_t *ptep, entry;
>> spinlock_t *ptl;
>> @@ -3883,8 +3884,7 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>> struct hstate *h = hstate_vma(vma);
>> struct address_space *mapping;
>> int need_wait_lock = 0;
>> -
>> - address &= huge_page_mask(h);
>> + unsigned long address = faddress & huge_page_mask(h);
>>
>> ptep = huge_pte_offset(mm, address, huge_page_size(h));
>> if (ptep) {
>> @@ -3914,7 +3914,7 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>>
>> entry = huge_ptep_get(ptep);
>> if (huge_pte_none(entry)) {
>> - ret = hugetlb_no_page(mm, vma, mapping, idx, address, ptep, flags);
>> + ret = hugetlb_no_page(mm, vma, mapping, idx, faddress, ptep, flags);
>> goto out_mutex;
>> }
>>
>> --
>> 2.16.1
>>
