On 21.08.25 22:29, David Hildenbrand wrote:

On 21.08.25 22:24, Linus Torvalds wrote:

quoted

On Thu, 21 Aug 2025 at 16:08, David Hildenbrand [off-list ref] wrote:

quoted

-       page = nth_page(page, offset >> PAGE_SHIFT);
+       page += offset / PAGE_SIZE;

Please keep the " >> PAGE_SHIFT" form.

No strong opinion.

I was primarily doing it to get rid of (in other cases) the parentheses.

Like in patch #29

-	/* Assumption: contiguous pages can be accessed as "page + i" */
-	page = nth_page(sg_page(sg), (*offset >> PAGE_SHIFT));
+	page = sg_page(sg) + *offset / PAGE_SIZE;

quoted

Is "offset" unsigned? Yes it is, But I had to look at the source code
to make sure, because it wasn't locally obvious from the patch. And
I'd rather we keep a pattern that is "safe", in that it doesn't
generate strange code if the value might be a 's64' (eg loff_t) on
32-bit architectures.

Because doing a 64-bit shift on x86-32 is like three cycles. Doing a
64-bit signed division by a simple constant is something like ten
strange instructions even if the end result is only 32-bit.

I would have thought that the compiler is smart enough to optimize that?
PAGE_SIZE is a constant.

It's late, I get your point: if the compiler can't optimize if it's a 
signed value ...

-- 
Cheers

David / dhildenb