Re: [PATCH v2] selftests/mm: skip hugetlb_dio tests when DIO alignment is incompatible

[Li Wang <liwang@redhat.com>]

On Fri, Mar 27, 2026 at 12:13:50PM -0700, Andrew Morton wrote:
> On Fri, 27 Mar 2026 20:03:05 +0800 Li Wang <liwang@redhat.com> wrote:
> 
> > hugetlb_dio test uses sub-page offsets (pagesize / 2) to verify that
> > hugepages used as DIO user buffers are correctly unpinned at completion.
> > 
> > However, on filesystems with a logical block size larger than half the
> > page size (e.g., 4K-sector block devices), these unaligned DIO writes
> > are rejected with -EINVAL, causing the test to fail unexpectedly.
> > 
> > Add get_dio_alignment() to query the filesystem's required DIO alignment
> > via statx(STATX_DIOALIGN) and pass it to run_dio_using_hugetlb(). Skip
> > individual test cases whose write length is not a multiple of the
> > alignment, so that aligned cases are still tested.
> > 
> > === Reproduce Steps ===
> > 
> >   # dd if=/dev/zero of=/tmp/test.img bs=1M count=512
> >   # losetup --sector-size 4096 /dev/loop0 /tmp/test.img
> >   # mkfs.xfs /dev/loop0
> >   # mkdir -p /mnt/dio_test
> >   # mount /dev/loop0 /mnt/dio_test
> > 
> >   // Modify test to open /mnt/dio_test and rebuild it:
> >   -       fd = open("/tmp", O_TMPFILE | O_RDWR | O_DIRECT, 0664);
> >   +       fd = open("/mnt/dio_test", O_TMPFILE | O_RDWR | O_DIRECT, 0664);
> > 
> >   # getconf PAGESIZE
> >   4096
> > 
> >   # echo 100 >/proc/sys/vm/nr_hugepages
> > 
> >   # ./hugetlb_dio
> >   TAP version 13
> >   1..4
> >   # No. Free pages before allocation : 100
> >   # No. Free pages after munmap : 100
> >   ok 1 free huge pages from 0-12288
> >   Bail out! Error writing to file
> >   : Invalid argument (22)
> >   # Planned tests != run tests (4 != 1)
> >   # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
> > 
> > ...
> >
> >     v2:
> >     	- Pass dio_align as a parameter to run_dio_using_hugetlb()
> >     	  instead of generally page_size/2 alignment check.
> > 
> 
> Whee, AI review has decided that pre glibc-2.36 is a problem (last time
> it was pre-2.37).

Ok, will handle this build issue with old glibc.

> And it's forgotten the previous fs-doesnt-support-DIO issues.  Did you
> alter that?

[Sorry, forgot to mention in change logs]

Yes, I added O_DIRECT flag back to the first open(). Then it'd skip into
a failure on filesystems that doesn't support O_DIRECT.

Also, statx on FS doesn't support DIO will set stx_dio_offset_align to 0,
which may led a division by zero issue, I added a zero check.

	} else if ((stx.stx_mask & STATX_DIOALIGN) &&
			stx.stx_dio_offset_align) {


> The get_dio_alignment-before-ksft_print_header thing seems legit.

+1

And, before sending v3, I would leave this patch for more days to
see if others comment.

-- 
Regards,
Li Wang