Re: [PATCH -next] ovl: respect underlying filesystem's get_unmapped_area()

[Matthew Wilcox <willy@infradead.org>]

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.