Re: [RFC PATCH v4 3/4] mm: add do_set_pte_range()

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

On 2/6/2023 10:44 PM, Matthew Wilcox wrote:
> On Mon, Feb 06, 2023 at 10:06:38PM +0800, Yin Fengwei wrote:
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index d6f8f41514cc..93192f04b276 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -1162,6 +1162,9 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
>>  
>>  vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page);
>>  void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr);
>> +void do_set_pte_range(struct vm_fault *vmf, struct folio *folio,
>> +		unsigned long addr, pte_t *pte,
>> +		unsigned long start, unsigned int nr);
> 
> There are only two callers of do_set_pte(), and they're both in mm.
> I don't think we should retain do_set_pte() as a wrapper, but rather
> change both callers to call 'set_pte_range()'.  The 'do' doesn't add
> any value, so let's drop that word.
OK.

> 
>> +	if (!cow) {
>> +		folio_add_file_rmap_range(folio, start, nr, vma, false);
>> +		add_mm_counter(vma->vm_mm, mm_counter_file(page), nr);
>> +	} else {
>> +		/*
>> +		 * rmap code is not ready to handle COW with anonymous
>> +		 * large folio yet. Capture and warn if large folio
>> +		 * is given.
>> +		 */
>> +		VM_WARN_ON_FOLIO(folio_test_large(folio), folio);
>> +	}
> 
> The handling of cow pages is still very clunky.
> folio_add_new_anon_rmap() handles anonymous large folios just fine.  I
> think David was looking at current code, not the code in mm-next.
OK. Let's wait for further comment from David.

> 
>> +		set_pte_at(vma->vm_mm, addr, pte, entry);
>> +
>> +		/* no need to invalidate: a not-present page won't be cached */
>> +		update_mmu_cache(vma, addr, pte);
>> +	} while (pte++, page++, addr += PAGE_SIZE, --nr > 0);
> 
> There's no need to speed-run this.  Let's do it properly and get the
Sorry. I don't get your point here. Do you mean the pte_next()? Or other
things?


Regards
Yin, Fengwei

> arch interface right.  This code isn't going to hit linux-next for four
> more weeks, which is plenty of time.