Re: [PATCH V9 3/7] io_uring: shrink io_mapped_buf

[Jens Axboe <axboe@kernel.dk>]

On 11/6/24 6:04 PM, Ming Lei wrote:
> On Wed, Nov 06, 2024 at 08:09:38AM -0700, Jens Axboe wrote:
>> On 11/6/24 5:26 AM, Ming Lei wrote:
>>> `struct io_mapped_buf` will be extended to cover kernel buffer which
>>> may be in fast IO path, and `struct io_mapped_buf` needs to be per-IO.
>>>
>>> So shrink sizeof(struct io_mapped_buf) by the following ways:
>>>
>>> - folio_shift is < 64, so 6bits are enough to hold it, the remained bits
>>>   can be used for the coming kernel buffer
>>>
>>> - define `acct_pages` as 'unsigned int', which is big enough for
>>>   accounting pages in the buffer
>>>
>>> Signed-off-by: Ming Lei <ming.lei@redhat.com>
>>> ---
>>>  io_uring/rsrc.c | 2 ++
>>>  io_uring/rsrc.h | 6 +++---
>>>  2 files changed, 5 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
>>> index 9b8827c72230..16f5abe03d10 100644
>>> --- a/io_uring/rsrc.c
>>> +++ b/io_uring/rsrc.c
>>> @@ -685,6 +685,8 @@ static bool io_try_coalesce_buffer(struct page ***pages, int *nr_pages,
>>>  		return false;
>>>  
>>>  	data->folio_shift = folio_shift(folio);
>>> +	WARN_ON_ONCE(data->folio_shift >= 64);
>>
>> Since folio_shift is 6 bits, how can that be try?
>>
>> I think you'd want:
>>
>> 	WARN_ON_ONCE(folio_shift(folio) >= 64);
>>
>> instead.
> 
> imu->folio_shift is 6 bits, and it is only copied from data->folio_shift(char),
> that is why the warning is added for data->folio_shift.

Ah yes that is fine then, for some reason I read that as 'data' being
an io_mapped_buffer.

-- 
Jens Axboe