Re: [PATCH -mm] mm, hugetlb: Pass fault address to no page handler

[Kirill A. Shutemov]

On Tue, May 15, 2018 at 08:57:56AM +0800, 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%
> 
> 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);

faddress? I would rather keep it address and rename maked out variable to
'haddr'. We use 'haddr' for the cause in other places.

-- 
 Kirill A. Shutemov