Re: [PATCH v4 34/36] rmap: add folio_add_file_rmap_range()

["Yin, Fengwei" <fengwei.yin@intel.com>]

Hi Ryan,

On 3/17/2023 12:34 AM, Ryan Roberts wrote:
> On 16/03/2023 16:27, Yin, Fengwei wrote:
>> Hi Matthew,
>>
>> On 3/16/2023 12:08 AM, Ryan Roberts wrote:
>>> On 15/03/2023 13:34, Ryan Roberts wrote:
>>>> On 15/03/2023 05:14, Matthew Wilcox (Oracle) wrote:
>>>>> From: Yin Fengwei <fengwei.yin@intel.com>
>>>>>
>>>>> folio_add_file_rmap_range() allows to add pte mapping to a specific
>>>>> range of file folio. Comparing to page_add_file_rmap(), it batched
>>>>> updates __lruvec_stat for large folio.
>>>>>
>>>>> Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
>>>>> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
>>>>> ---
>>>>>  include/linux/rmap.h |  2 ++
>>>>>  mm/rmap.c            | 60 +++++++++++++++++++++++++++++++++-----------
>>>>>  2 files changed, 48 insertions(+), 14 deletions(-)
>>>>>
>>>>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
>>>>> index b87d01660412..a3825ce81102 100644
>>>>> --- a/include/linux/rmap.h
>>>>> +++ b/include/linux/rmap.h
>>>>> @@ -198,6 +198,8 @@ void folio_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
>>>>>  		unsigned long address);
>>>>>  void page_add_file_rmap(struct page *, struct vm_area_struct *,
>>>>>  		bool compound);
>>>>> +void folio_add_file_rmap_range(struct folio *, struct page *, unsigned int nr,
>>>>> +		struct vm_area_struct *, bool compound);
>>>>>  void page_remove_rmap(struct page *, struct vm_area_struct *,
>>>>>  		bool compound);
>>>>>  
>>>>> diff --git a/mm/rmap.c b/mm/rmap.c
>>>>> index 4898e10c569a..a91906b28835 100644
>>>>> --- a/mm/rmap.c
>>>>> +++ b/mm/rmap.c
>>>>> @@ -1301,31 +1301,39 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
>>>>>  }
>>>>>  
>>>>>  /**
>>>>> - * page_add_file_rmap - add pte mapping to a file page
>>>>> - * @page:	the page to add the mapping to
>>>>> + * folio_add_file_rmap_range - add pte mapping to page range of a folio
>>>>> + * @folio:	The folio to add the mapping to
>>>>> + * @page:	The first page to add
>>>>> + * @nr_pages:	The number of pages which will be mapped
>>>>>   * @vma:	the vm area in which the mapping is added
>>>>>   * @compound:	charge the page as compound or small page
>>>>>   *
>>>>> + * The page range of folio is defined by [first_page, first_page + nr_pages)
>>>>> + *
>>>>>   * The caller needs to hold the pte lock.
>>>>>   */
>>>>> -void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
>>>>> -		bool compound)
>>>>> +void folio_add_file_rmap_range(struct folio *folio, struct page *page,
>>>>> +			unsigned int nr_pages, struct vm_area_struct *vma,
>>>>> +			bool compound)
>>>>>  {
>>>>> -	struct folio *folio = page_folio(page);
>>>>>  	atomic_t *mapped = &folio->_nr_pages_mapped;
>>>>> -	int nr = 0, nr_pmdmapped = 0;
>>>>> -	bool first;
>>>>> +	unsigned int nr_pmdmapped = 0, first;
>>>>> +	int nr = 0;
>>>>>  
>>>>> -	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
>>>>> +	VM_WARN_ON_FOLIO(compound && !folio_test_pmd_mappable(folio), folio);
>>>>>  
>>>>>  	/* Is page being mapped by PTE? Is this its first map to be added? */
>>>>>  	if (likely(!compound)) {
>>>>> -		first = atomic_inc_and_test(&page->_mapcount);
>>>>> -		nr = first;
>>>>> -		if (first && folio_test_large(folio)) {
>>>>> -			nr = atomic_inc_return_relaxed(mapped);
>>>>> -			nr = (nr < COMPOUND_MAPPED);
>>>>> -		}
>>>>> +		do {
>>>>> +			first = atomic_inc_and_test(&page->_mapcount);
>>>>> +			if (first && folio_test_large(folio)) {
>>>>> +				first = atomic_inc_return_relaxed(mapped);
>>>>> +				first = (nr < COMPOUND_MAPPED);
>>>>
>>>> This still contains the typo that Yin Fengwei spotted in the previous version:
>>>> https://lore.kernel.org/linux-mm/20230228213738.272178-1-willy@infradead.org/T/#m84673899e25bc31356093a1177941f2cc35e5da8
>>>>
>>>> FYI, I'm seeing a perf regression of about 1% when compiling the kernel on
>>>> Ampere Altra (arm64) with this whole series on top of v6.3-rc1 (In a VM using
>>>> ext4 filesystem). Looks like instruction aborts are taking much longer and a
>>>> selection of syscalls are a bit slower. Still hunting down the root cause. Will
>>>> report once I have conclusive diagnosis.
>>>
>>> I'm sorry - I'm struggling to find the exact cause. But its spending over 2x the
>>> amount of time in the instruction abort handling code once patches 32-36 are
>>> included. Everything in the flame graph is just taking longer. Perhaps we are
>>> getting more instruction aborts somehow? I have the flamegraphs if anyone wants
>>> them - just shout and I'll email them separately.
>> Thanks a lot to Ryan for sharing the flamegraphs to me. I found the __do_fault()
>> is called with patch 32-36 while no __do_fault() just with first 31 patches. I 
>> suspect the folio_add_file_rmap_range() missed some PTEs population. Please give
>> me few days to find the root cause and fix. Sorry for this.
> 
> You're welcome. Give me a shout once you have a re-spin and I'll rerun the tests.
Could you please help to try following changes? Thanks in advance.

diff --git a/mm/filemap.c b/mm/filemap.c
index 40be33b5ee46..137011320c68 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3504,15 +3504,16 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
 		if (!pte_none(vmf->pte[count]))
 			goto skip;
 
-		if (vmf->address == addr)
-			ret = VM_FAULT_NOPAGE;
-
 		count++;
 		continue;
 skip:
 		if (count) {
 			set_pte_range(vmf, folio, page, count, addr);
 			folio_ref_add(folio, count);
+			if ((vmf->address < (addr + count * PAGE_SIZE)) &&
+					(vmf->address >= addr))
+				ret = VM_FAULT_NOPAGE;
+
 		}
 
 		count++;
@@ -3525,6 +3526,9 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
 	if (count) {
 		set_pte_range(vmf, folio, page, count, addr);
 		folio_ref_add(folio, count);
+		if ((vmf->address < (addr + count * PAGE_SIZE)) &&
+				(vmf->address >= addr))
+			ret = VM_FAULT_NOPAGE;
 	}
 
 	vmf->pte = old_ptep;


Regards
Yin, Fengwei

> 
>>
>>
>> Regards
>> Yin, Fengwei
>>
>>>
>>>>
>>>> Thanks,
>>>> Ryan
>>>>
>>>>
>>>>> +			}
>>>>> +
>>>>> +			if (first)
>>>>> +				nr++;
>>>>> +		} while (page++, --nr_pages > 0);
>>>>>  	} else if (folio_test_pmd_mappable(folio)) {
>>>>>  		/* That test is redundant: it's for safety or to optimize out */
>>>>>  
>>>>> @@ -1354,6 +1362,30 @@ void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
>>>>>  	mlock_vma_folio(folio, vma, compound);
>>>>>  }
>>>>>  
>>>>> +/**
>>>>> + * page_add_file_rmap - add pte mapping to a file page
>>>>> + * @page:	the page to add the mapping to
>>>>> + * @vma:	the vm area in which the mapping is added
>>>>> + * @compound:	charge the page as compound or small page
>>>>> + *
>>>>> + * The caller needs to hold the pte lock.
>>>>> + */
>>>>> +void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
>>>>> +		bool compound)
>>>>> +{
>>>>> +	struct folio *folio = page_folio(page);
>>>>> +	unsigned int nr_pages;
>>>>> +
>>>>> +	VM_WARN_ON_ONCE_PAGE(compound && !PageTransHuge(page), page);
>>>>> +
>>>>> +	if (likely(!compound))
>>>>> +		nr_pages = 1;
>>>>> +	else
>>>>> +		nr_pages = folio_nr_pages(folio);
>>>>> +
>>>>> +	folio_add_file_rmap_range(folio, page, nr_pages, vma, compound);
>>>>> +}
>>>>> +
>>>>>  /**
>>>>>   * page_remove_rmap - take down pte mapping from a page
>>>>>   * @page:	page to remove mapping from
>>>>
>>>
> 
>