Re: [PATCH] hmm-tests: Fix migrate_dirty_page test

[David Hildenbrand]

On 13.09.22 10:20, Alistair Popple wrote:
> David Hildenbrand <david@xxxxxxxxxx> writes:
>
> > On 13.09.22 07:22, Alistair Popple wrote:
> > > As noted by John Hubbard the original test relied on side effects of the
> > > implementation of migrate_vma_setup() to detect if pages had been
> > > swapped to disk or not. This is subject to change in future so
> > > explicitly check for swap entries via pagemap instead. Fix a spelling
> > > mistake while we're at it.
> > > Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>
> > > Fixes: 5cc88e844e87 ("selftests/hmm-tests: add test for dirty bits")
> > > ---
> > >    tools/testing/selftests/vm/hmm-tests.c | 50 +++++++++++++++++++++++---
> > >    1 file changed, 46 insertions(+), 4 deletions(-)
> > > diff --git a/tools/testing/selftests/vm/hmm-tests.c
> > > b/tools/testing/selftests/vm/hmm-tests.c
> > > index 70fdb49b59ed..b5f6a7dc1f12 100644
> > > --- a/tools/testing/selftests/vm/hmm-tests.c
> > > +++ b/tools/testing/selftests/vm/hmm-tests.c
> > > @@ -1261,9 +1261,47 @@ static int destroy_cgroup(void)
> > >    	return 0;
> > >    }
> > >    +static uint64_t get_pfn(int fd, uint64_t ptr)
> > > +{
> > > +	uint64_t pfn;
> > > +	int ret;
> > > +
> > > +	ret = pread(fd, &pfn, sizeof(ptr),
> > > +		(uint64_t) ptr / getpagesize() * sizeof(ptr));
> > > +	if (ret != sizeof(ptr))
> > > +		return 0;
> > > +
> > > +	return pfn;
> > > +}
> > > +
> > > +#define PAGEMAP_SWAPPED (1ULL << 62)
> > > +
> > > +/* Returns true if at least one page in the range is on swap */
> > > +static bool pages_swapped(void *ptr, unsigned long pages)
> > > +{
> > > +	uint64_t pfn;
> > > +	int fd = open("/proc/self/pagemap", O_RDONLY);
> > > +	unsigned long i;
> > > +
> > > +	if (fd < 0)
> > > +		return false;
> > > +
> > > +	for (i = 0; i < pages; i++) {
> > > +		pfn = get_pfn(fd, (uint64_t) ptr + i * getpagesize());
> > > +
> > > +		if (pfn & PAGEMAP_SWAPPED) {
> > > +			close(fd);
> > > +			return true;
> > > +		}
> >
> > We do have pagemap_get_entry() in vm_util.c to query the pagemap entry.
>
> Thanks. I'd missed that, although `grep pagemap
> tools/testing/selftests/vm` suggests I'm not the first to follow a
> tradition of open-coding this :-)
>
> But there's no need to perpetuate that tradition, so will redo this to
> use vm_util.c instead.

Yeah, we just recently factored stuff out into there. I'll be factoring 
out more in my upcoming tests from the madv_populate tests.

--
Thanks,

David / dhildenb