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

[Jens Axboe <axboe@kernel.dk>]

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.

And agree that acct_pages doesn't need to be an unsigned long.

-- 
Jens Axboe