On 2/1/2023 10:34 PM, Kirill A. Shutemov wrote:
> On Wed, Feb 01, 2023 at 04:17:33PM +0800, Yin Fengwei wrote:
>> The shared fault handler can also benefit from fault-around. While it
>> is uncommon to write to MAP_SHARED files, applications that do will see
>> a huge benefit with will-it-scale:page_fault3 (shared file write fault)
>> improving by 375%.
>>
>> Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
>> Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
>> ---
>> mm/memory.c | 11 +++++++++++
>> 1 file changed, 11 insertions(+)
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 7a04a1130ec1..51c04bb60724 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -4546,6 +4546,17 @@ static vm_fault_t do_shared_fault(struct vm_fault *vmf)
>> struct vm_area_struct *vma = vmf->vma;
>> vm_fault_t ret, tmp;
>>
>> + /*
>> + * Let's call ->map_pages() first and use ->fault() as fallback
>> + * if page by the offset is not ready to be mapped (cold cache or
>> + * something).
>> + */
>> + if (should_fault_around(vmf)) {
>> + ret = do_fault_around(vmf);
>> + if (ret)
>> + return ret;
>> + }
>> +
>
> I believe it bypasses ->page_mkwrite() completely, no?
>
> So you get a writable PTEs without notifying the filesystem. Smells like a
> data loss.
Yes. You are right. This may be the reason why fault around is not enabled
for shared file write fault? I will drop this patch. Thanks.
Regards
Yin, Fengwei
>
>> ret = __do_fault(vmf);
>> if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
>> return ret;
>> --
>> 2.30.2
>>
>>
>
