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

["Huang\, Ying" <ying.huang@intel.com>]

Michal Hocko <mhocko@kernel.org> writes:

> On Thu 17-05-18 16:35:39, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@intel.com>
>> 
>> 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?

Sure.  I will try to get some number for that kind of workload.

Best Regards,
Huang, Ying

> 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@intel.com>
>> Cc: Andrea Arcangeli <aarcange@redhat.com>
>> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>> Cc: Andi Kleen <andi.kleen@intel.com>
>> Cc: Jan Kara <jack@suse.cz>
>> Cc: Matthew Wilcox <mawilcox@microsoft.com>
>> Cc: Hugh Dickins <hughd@google.com>
>> Cc: Minchan Kim <minchan@kernel.org>
>> Cc: Shaohua Li <shli@fb.com>
>> Cc: Christopher Lameter <cl@linux.com>
>> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
>> Cc: Punit Agrawal <punit.agrawal@arm.com>
>> Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
>> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
>> Acked-by: David Rientjes <rientjes@google.com>
>> Acked-by: Michal Hocko <mhocko@suse.com>
>> ---
>>  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
>>