Re: [PATCH 4/4] aio: use iovec array rather than the single one

[Gu Zheng <guz.fnst@cn.fujitsu.com>]

Hi Jeff,
On 07/22/2014 11:20 PM, Jeff Moyer wrote:

> Gu Zheng <guz.fnst@cn.fujitsu.com> writes:
> 
>> use an iovec array rather than the single one, so that we can avoid
>> to alloc more iovecs buffer in small(< 8) PREADV/PWRITEV cases.
> 
> I did some basic functional testing of this change and the change in
> patch 1/4.  That testing included using aio-stress to drive queue depths
> of 7, 8 and 9, and verify that it didn't fall over.  I also ran xfstests
> './check -g aio', and libaio's 'make partcheck'.

> 
> The change looks good to me, and passed testing, so:
> 
> Reviewed-by: Jeff Moyer <jmoyer@redhat.com>

Thanks for your review and test.

> 
> However, I still would like some comment on the reasoning behind it, and
> whether there is some measurable performance advantage for some
> workload.  Additionally, it would be nice if that comment made its way
> into the commit message.

I'll add more useful info, and send it out later.

Thanks,
Gu

> 
> Cheers,
> Jeff
> 
>>
>> Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
>> ---
>>  fs/aio.c |   10 +++++-----
>>  1 files changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/aio.c b/fs/aio.c
>> index 0cd0479..ef21efe 100644
>> --- a/fs/aio.c
>> +++ b/fs/aio.c
>> @@ -1260,12 +1260,12 @@ static ssize_t aio_setup_vectored_rw(struct kiocb *kiocb,
>>  	if (compat)
>>  		ret = compat_rw_copy_check_uvector(rw,
>>  				(struct compat_iovec __user *)buf,
>> -				*nr_segs, 1, *iovec, iovec);
>> +				*nr_segs, UIO_FASTIOV, *iovec, iovec);
>>  	else
>>  #endif
>>  		ret = rw_copy_check_uvector(rw,
>>  				(struct iovec __user *)buf,
>> -				*nr_segs, 1, *iovec, iovec);
>> +				*nr_segs, UIO_FASTIOV, *iovec, iovec);
>>  	if (ret < 0)
>>  		return ret;
>>  
>> @@ -1302,7 +1302,7 @@ static ssize_t aio_run_iocb(struct kiocb *req, unsigned opcode,
>>  	fmode_t mode;
>>  	aio_rw_op *rw_op;
>>  	rw_iter_op *iter_op;
>> -	struct iovec inline_vec, *iovec = &inline_vec;
>> +	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
>>  	struct iov_iter iter;
>>  
>>  	switch (opcode) {
>> @@ -1337,7 +1337,7 @@ rw_common:
>>  		if (!ret)
>>  			ret = rw_verify_area(rw, file, &req->ki_pos, req->ki_nbytes);
>>  		if (ret < 0) {
>> -			if (iovec != &inline_vec)
>> +			if (iovec != inline_vecs)
>>  				kfree(iovec);
>>  			return ret;
>>  		}
>> @@ -1384,7 +1384,7 @@ rw_common:
>>  		return -EINVAL;
>>  	}
>>  
>> -	if (iovec != &inline_vec)
>> +	if (iovec != inline_vecs)
>>  		kfree(iovec);
>>  
>>  	if (ret != -EIOCBQUEUED) {
> .
>