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?
Thanks.
