On Thu, Feb 13, 2020 at 06:44:19PM +0300, Kirill A. Shutemov wrote: > On Tue, Feb 11, 2020 at 08:18:31PM -0800, Matthew Wilcox wrote: > > From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> > > > > If the page is compound, check the appropriate indices and return the > > appropriate sizes. > > Is it guarnteed that the page is never called on tail page? I think so. page_mkwrite_check_truncate() is only called on pages which belong to a particular filesystem. Only filesystems which have the FS_LARGE_PAGES flag set will have compound pages allocated in the page cache for their files. As filesystems are converted, they will only see large head pages. I'll happily put in a VM_BUG_ON(PageTail(page), page); to ensure we don't screw that up.
