Re: [PATCH -next] mm/filemap: fix that first page is not mark accessed in filemap_read()

[Yu Kuai <yukuai3@huawei.com>]

On 2022/06/03 2:22, Andrew Morton wrote:
> On Thu, 2 Jun 2022 16:21:29 +0800 Yu Kuai <yukuai3@huawei.com> wrote:
> 
>> In filemap_read(), 'ra->prev_pos' is set to 'iocb->ki_pos + copied',
>> while it should be 'iocb->ki_ops'. For consequence,
>> folio_mark_accessed() will not be called for 'fbatch.folios[0]' since
>> 'iocb->ki_pos' is always equal to 'ra->prev_pos'.
>>
>> ...
>>
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -2728,10 +2728,11 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
>>   				flush_dcache_folio(folio);
>>   
>>   			copied = copy_folio_to_iter(folio, offset, bytes, iter);
>> -
>> -			already_read += copied;
>> -			iocb->ki_pos += copied;
>> -			ra->prev_pos = iocb->ki_pos;
>> +			if (copied) {
>> +				ra->prev_pos = iocb->ki_pos;
>> +				already_read += copied;
>> +				iocb->ki_pos += copied;
>> +			}
>>   
>>   			if (copied < bytes) {
>>   				error = -EFAULT;
> 
> It seems tidier, but does it matter?  If copied==0 we're going to break
> out and return -EFAULT anyway?
Hi,

Please notice that I set 'prev_ops' to 'ki_pos' first here, instead of
'ki_pos + copied'.

Thanks,
Kuai
> .
>