Re: [PATCH] mm: Improve PageAnon() to check the whole PAGE_MAPPING_FLAGS

[David Hildenbrand <david@redhat.com>]

On 15.11.19 06:59, lixinhai.lxh@gmail.com wrote:
> On 2019-11-15 at 11:18 Li Xinhai wrote:
>> PageAnon() just checking on PAGE_MAPPING_ANON bit would cause page,
>> with PageKsm as true, been wrongly considered as PageAnon. Now,
>> checking the whole PAGE_MAPPING_FLAGS to avoid this error.
>>
>> Reported from:
>> https://lore.kernel.org/linux-mm/20191113000651.20677-1-rcampbell@nvidia.com/
>>
>> Reported-by: Ralph Campbell <rcampbell@nvidia.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
>> ---
>> include/linux/page-flags.h | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
>> index 1bf83c8..1849fc3 100644
>> --- a/include/linux/page-flags.h
>> +++ b/include/linux/page-flags.h
>> @@ -461,7 +461,8 @@ static __always_inline int PageMappingFlags(struct page *page)
>> static __always_inline int PageAnon(struct page *page)
>> {
>> page = compound_head(page);
>> -	return ((unsigned long)page->mapping & PAGE_MAPPING_ANON) != 0;
>> +	return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
>> +	PAGE_MAPPING_ANON;
>> }
>>
>> static __always_inline int __PageMovable(struct page *page)
>> --
>> 1.8.3.1
>>
> 
> The current semantics of PageAnon() for both KSM and !KSM are used in many 
> places, so can't change it alone without change other code.
> Need skip this patch.

... I assume that was intended because KSM only merges anonymous pages?
If it was not intended, it would scream for a cleanup.

> 
> - Xinhai
> 


-- 

Thanks,

David / dhildenb