On Mon, Mar 07, 2016 at 10:03:36AM +1100, Dave Chinner wrote: > On Sun, Mar 06, 2016 at 03:30:34AM +0300, Kirill A. Shutemov wrote: > > On Sun, Mar 06, 2016 at 09:38:11AM +1100, Dave Chinner wrote: > > > And it's not just hole punching that has this problem. Direct IO is > > > going to have the same issue with invalidation of the mapped ranges > > > over the IO being done. XFS already WARNs when page cache > > > invalidation fails with EBUSY in direct IO, because that is > > > indicative of an application with a potential data corruption vector > > > and there's nothing we can do in the kernel code to prevent it. > > > > My current understanding is that for filesystems with persistent storage, > > in order to make THP any useful, we would need to implement writeback > > without splitting the huge page. > > Algorithmically it is no different to filesytem block size < page > size writeback. > > > At the moment, I have no idea how hard it would be.. > > THP support would effectively require us to remove PAGE_CACHE_SIZE > assumptions from all of the filesystem and buffer code. That's a > large chunk of work e.g. fs/buffer.c and any filesystem that uses > bufferheads for tracking filesystem block state through the page > cache.
I'll try to learn more about the code before the summit. I guess it's something worth descussion in person. -- Kirill A. Shutemov
