Re: [PATCH] block: shift with PAGE_SHIFT instead of dividing with PAGE_SIZE

On 2/22/23 9:25 AM, Pankaj Raghav wrote:

On 2023-02-22 20:57, Bart Van Assche wrote:

quoted

On 2/22/23 06:34, Pankaj Raghav wrote:

quoted

No functional change. Division will be costly, especially in the hot
path (page_is_mergeable() and bio_copy_user_iov())

Although the change looks fine to me, is there any compiler for which this
patch makes a difference? I would expect that a compiler performs this
optimization even without this patch.

I didn't notice any for x86_64. But I was thinking this also as a way to
maintain consistency across block code where we do a shift with PAGE_SHIFT
instead of dividing with PAGE_SIZE.

It won't make a difference on any architecture, it'd be a pretty
awful compiler that didn't turn a division by a constant power-of-2
into a shift.

-- 
Jens Axboe