21 Aug
2025
21 Aug
'25
8:24 p.m.
On Thu, 21 Aug 2025 at 16:08, David Hildenbrand david@redhat.com wrote:
page = nth_page(page, offset >> PAGE_SHIFT);
page += offset / PAGE_SIZE;
Please keep the " >> PAGE_SHIFT" form.
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.
And again - not the case *here*, but just a general "let's keep to one pattern", and the shift pattern is simply the better choice.
Linus