Re: [PATCH -V2 -mm] mm, hugetlbfs: Pass fault address to no page handler

[Michal Hocko]

On Thu 17-05-18 16:35:39, Huang, Ying wrote:
> From: Huang Ying <ying.huang@xxxxxxxxx>
> 
> This is to take better advantage of general huge page clearing
> optimization (c79b57e462b5d, "mm: hugetlb: clear target sub-page last
> when clearing huge page") for hugetlbfs.  In the general optimization
> patch, the sub-page to access will be cleared last to avoid the cache
> lines of to access sub-page to be evicted when clearing other
> sub-pages.  This works better if we have the address of the sub-page
> to access, that is, the fault address inside the huge page.  So the
> hugetlbfs no page fault handler is changed to pass that information.
> This will benefit workloads which don't access the begin of the
> hugetlbfs huge page after the page fault under heavy cache contention
> for shared last level cache.
> 
> The patch is a generic optimization which should benefit quite some
> workloads, not for a specific use case.  To demonstrate the performance
> benefit of the patch, we tested it with vm-scalability run on
> hugetlbfs.
> 
> 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 mmaps a big anonymous memory area with MAP_HUGETLB 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%.

OK, this description is much better. Thanks! I would still like to see
the benefit on more realistic workloads. Those tends to be more towards
large pre-allocated mappings AFAIK (something like a DB start). Can you
add those numbers?

Btw. I do not mind the address->haddr change to be more in sync with THP
but the previous patch was much more easier to review. Now you have to
go to the code and check there are no unintended leftovers. So it would
have been better to split that into two patches but I will not insist.

> 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: 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>
> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
>  mm/hugetlb.c | 42 +++++++++++++++++++++---------------------
>  1 file changed, 21 insertions(+), 21 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 129088710510..4f0682cb9414 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -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 haddr = address & huge_page_mask(h);
>  
>  	/*
>  	 * Currently, we are forced to kill the process in the event the
> @@ -3716,7 +3717,7 @@ static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  			u32 hash;
>  			struct vm_fault vmf = {
>  				.vma = vma,
> -				.address = address,
> +				.address = haddr,
>  				.flags = flags,
>  				/*
>  				 * Hard to debug if it ends up being
> @@ -3733,14 +3734,14 @@ static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  			 * fault to make calling code simpler.
>  			 */
>  			hash = hugetlb_fault_mutex_hash(h, mm, vma, mapping,
> -							idx, address);
> +							idx, haddr);
>  			mutex_unlock(&hugetlb_fault_mutex_table[hash]);
>  			ret = handle_userfault(&vmf, VM_UFFD_MISSING);
>  			mutex_lock(&hugetlb_fault_mutex_table[hash]);
>  			goto out;
>  		}
>  
> -		page = alloc_huge_page(vma, address, 0);
> +		page = alloc_huge_page(vma, haddr, 0);
>  		if (IS_ERR(page)) {
>  			ret = PTR_ERR(page);
>  			if (ret == -ENOMEM)
> @@ -3789,12 +3790,12 @@ static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  	 * the spinlock.
>  	 */
>  	if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
> -		if (vma_needs_reservation(h, vma, address) < 0) {
> +		if (vma_needs_reservation(h, vma, haddr) < 0) {
>  			ret = VM_FAULT_OOM;
>  			goto backout_unlocked;
>  		}
>  		/* Just decrements count, does not deallocate */
> -		vma_end_reservation(h, vma, address);
> +		vma_end_reservation(h, vma, haddr);
>  	}
>  
>  	ptl = huge_pte_lock(h, mm, ptep);
> @@ -3808,17 +3809,17 @@ static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  
>  	if (anon_rmap) {
>  		ClearPagePrivate(page);
> -		hugepage_add_new_anon_rmap(page, vma, address);
> +		hugepage_add_new_anon_rmap(page, vma, haddr);
>  	} else
>  		page_dup_rmap(page, true);
>  	new_pte = make_huge_pte(vma, page, ((vma->vm_flags & VM_WRITE)
>  				&& (vma->vm_flags & VM_SHARED)));
> -	set_huge_pte_at(mm, address, ptep, new_pte);
> +	set_huge_pte_at(mm, haddr, ptep, new_pte);
>  
>  	hugetlb_count_add(pages_per_huge_page(h), mm);
>  	if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
>  		/* Optimization, do the COW without a second fault */
> -		ret = hugetlb_cow(mm, vma, address, ptep, page, ptl);
> +		ret = hugetlb_cow(mm, vma, haddr, ptep, page, ptl);
>  	}
>  
>  	spin_unlock(ptl);
> @@ -3830,7 +3831,7 @@ static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  	spin_unlock(ptl);
>  backout_unlocked:
>  	unlock_page(page);
> -	restore_reserve_on_error(h, vma, address, page);
> +	restore_reserve_on_error(h, vma, haddr, page);
>  	put_page(page);
>  	goto out;
>  }
> @@ -3883,10 +3884,9 @@ 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;
> +	unsigned long haddr = address & huge_page_mask(h);
>  
> -	address &= huge_page_mask(h);
> -
> -	ptep = huge_pte_offset(mm, address, huge_page_size(h));
> +	ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
>  	if (ptep) {
>  		entry = huge_ptep_get(ptep);
>  		if (unlikely(is_hugetlb_entry_migration(entry))) {
> @@ -3896,20 +3896,20 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>  			return VM_FAULT_HWPOISON_LARGE |
>  				VM_FAULT_SET_HINDEX(hstate_index(h));
>  	} else {
> -		ptep = huge_pte_alloc(mm, address, huge_page_size(h));
> +		ptep = huge_pte_alloc(mm, haddr, huge_page_size(h));
>  		if (!ptep)
>  			return VM_FAULT_OOM;
>  	}
>  
>  	mapping = vma->vm_file->f_mapping;
> -	idx = vma_hugecache_offset(h, vma, address);
> +	idx = vma_hugecache_offset(h, vma, haddr);
>  
>  	/*
>  	 * Serialize hugepage allocation and instantiation, so that we don't
>  	 * get spurious allocation failures if two CPUs race to instantiate
>  	 * the same page in the page cache.
>  	 */
> -	hash = hugetlb_fault_mutex_hash(h, mm, vma, mapping, idx, address);
> +	hash = hugetlb_fault_mutex_hash(h, mm, vma, mapping, idx, haddr);
>  	mutex_lock(&hugetlb_fault_mutex_table[hash]);
>  
>  	entry = huge_ptep_get(ptep);
> @@ -3939,16 +3939,16 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>  	 * consumed.
>  	 */
>  	if ((flags & FAULT_FLAG_WRITE) && !huge_pte_write(entry)) {
> -		if (vma_needs_reservation(h, vma, address) < 0) {
> +		if (vma_needs_reservation(h, vma, haddr) < 0) {
>  			ret = VM_FAULT_OOM;
>  			goto out_mutex;
>  		}
>  		/* Just decrements count, does not deallocate */
> -		vma_end_reservation(h, vma, address);
> +		vma_end_reservation(h, vma, haddr);
>  
>  		if (!(vma->vm_flags & VM_MAYSHARE))
>  			pagecache_page = hugetlbfs_pagecache_page(h,
> -								vma, address);
> +								vma, haddr);
>  	}
>  
>  	ptl = huge_pte_lock(h, mm, ptep);
> @@ -3973,16 +3973,16 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
>  
>  	if (flags & FAULT_FLAG_WRITE) {
>  		if (!huge_pte_write(entry)) {
> -			ret = hugetlb_cow(mm, vma, address, ptep,
> +			ret = hugetlb_cow(mm, vma, haddr, ptep,
>  					  pagecache_page, ptl);
>  			goto out_put_page;
>  		}
>  		entry = huge_pte_mkdirty(entry);
>  	}
>  	entry = pte_mkyoung(entry);
> -	if (huge_ptep_set_access_flags(vma, address, ptep, entry,
> +	if (huge_ptep_set_access_flags(vma, haddr, ptep, entry,
>  						flags & FAULT_FLAG_WRITE))
> -		update_mmu_cache(vma, address, ptep);
> +		update_mmu_cache(vma, haddr, ptep);
>  out_put_page:
>  	if (page != pagecache_page)
>  		unlock_page(page);
> -- 
> 2.16.1
> 

-- 
Michal Hocko
SUSE Labs