On Wed 26-03-25 11:50:55, Luis Chamberlain wrote:

0-day reported a page migration kernel warning with folios which happen
to be buffer-heads [0]. I'm having a terribly hard time reproducing the bug
and so I wrote this test to force page migration filesystems.

It turns out we have have no tests for page migration on fstests or ltp,
and its no surprise, other than compaction covered by generic/750 there
is no easy way to trigger page migration right now unless you have a
numa system.

We should evaluate if we want to help stress test page migration
artificially by later implementing a way to do page migration on simple
systems to an artificial target.

So far, this doesn't trigger any kernel splats, not even warnings for me.

Reported-by: kernel test robot <redacted>
Link: https://lore.kernel.org/r/202503101536.27099c77-lkp@intel.com (local) # [0]
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

So when I was testing page migration in the past MM guys advised me to use
THP compaction as a way to trigger page migration. You can manually
trigger compaction by:

echo 1 >/proc/sys/vm/compact_memory

So you first mess with the page cache a bit to fragment memory and then
call the above to try to compact it back...

								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR