On 11/12/24 2:12 AM, Kirill A. Shutemov wrote: > On Mon, Nov 11, 2024 at 04:37:30PM -0700, Jens Axboe wrote: >> Add a page flag that file IO can use to indicate that the IO being done >> is uncached, as in it should not persist in the page cache after the IO >> has been completed. > > I have not found a way to avoid using a new bit. I am unsure if we have > enough bits on 32-bit systems with all possible features enabled. I think it should be OK, at least the kernel test bot reports build success on all the archs it tests, which has a lot of 32-bit archs. I have to say I didn't check on numbering and if the mm subsystem has a BUILD_BUG_ON() for bits exceeding the allowable value for unsigned long on the host, but I'm assuming it does? > In the worst-case scenario, we may need to make the feature 64-bit only. > I believe it should be acceptable as long as userspace is prepared for the > possibility that RWF_UNCACHED may fail. It is not going to be supported by > all filesystems anyway. Right, I would not even see that as a big issue. 32-bit would just see -EOPNOTSUPP for any fs, even ones that support it on 64-bit archs. -- Jens Axboe
