On Thu, Mar 27, 2025 at 12:53:30PM +0100, Jan Kara wrote: > 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 <oliver.sang@xxxxxxxxx> > > Link: https://lore.kernel.org/r/202503101536.27099c77-lkp@xxxxxxxxx # [0] > > Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx> > > 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 Right, that's what generic/750 does. IT runs fsstress and every 5 seconds runs memory compaction in the background. > So you first mess with the page cache a bit to fragment memory and then > call the above to try to compact it back... Which is effectively what g/750 tries to exercise. When it's run by check-parallel, compaction ends up doing a lot more work over a much wider range of tests... -Dave. -- Dave Chinner david@xxxxxxxxxxxxx
