On Tue, Dec 10, 2024 at 03:13:21PM +0800, Jinjiang Tu wrote: > 在 2024/12/9 21:33, Matthew Wilcox 写道: > > On Mon, Dec 09, 2024 at 02:43:08PM +0800, Jinjiang Tu wrote: > > > 在 2024/12/6 21:58, Matthew Wilcox 写道: > > > > On Thu, Dec 05, 2024 at 10:30:38PM +0800, Jinjiang Tu wrote: > > > > > During our tests in containers, there is a read-only file (i.e., shared > > > > Show your test. > > > I mmap an overlayfs file with PROT_READ, and call madvise(MADV_COLLAPSE), the code > > > is as follows: > > > > > > fd = open(path, O_RDONLY); > > > addr = mmap(NULL, size, PROT_READ, MAP_PRIVATE, fd, 0); > > > ret = madvise(addr, size, MADV_COLLAPSE); > > > > > > The addr isn't THP-aligned and ret is -1, errno is EINVAL. > > Then your test is buggy. > > > > * Check alignment for file vma and size for both file and anon vma by > > * filtering out the unsuitable orders. > > > > You didn't align your mmap, so it's expected to fail. > > When mmap an ext4 file, since ext4_file_operations defines ".get_unmapped_area = thp_get_unmapped_area", it calls thp_get_unmapped_area() in __get_unmapped_area to > mmap at a THP-aligned address. > > For overlayfs file, it's underlying filesystem may be ext4, which supports large folio. For this situation, should we mmap at a THP-aligned address too, to map > THP? Actually, ext4 doesn't support large folios. thp_get_unmapped_area() was added for DAX in 2016 (dbe6ec815641).
