On 2024/12/11 1:58, Matthew Wilcox wrote: > 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. > I have sent out two series to enable ext4 support for large folios. Feel free to give it a try. https://lore.kernel.org/linux-ext4/20241022111059.2566137-1-yi.zhang@xxxxxxxxxxxxxxx/ https://lore.kernel.org/linux-ext4/20241125114419.903270-1-yi.zhang@xxxxxxxxxxxxxxx/ Thanks, Yi.
