Christoph, Am 12.05.2016 um 13:49 schrieb Christoph Hellwig: > Hi Richard, > > the series looks fine to me, but it fails to address the root cause: Is this a Reviewed-by? :-) > that we have an inherently dangerous default for ->migratepage that > assumes that file systems are implemented a certain way. I think the > series should also grow a third patch to remove the default and just > wire it up for the known good file systems, although we'd need some > input on what known good is. > > Any idea what filesystems do get regular testing with code that's using > CMA? A good approximation might be those that use the bufer_head > based aops from fs/buffer.c No idea how much is being tested. I fear most issues are unknown. At least for UBIFS it took years to get aware of the issue. Thanks again to Maxime and Boris for providing a reproducer. There are two classes of issues: a) filesystems that use buffer_migrate_page() but shouldn't b) filesystems that don't implement ->migratepage() and fallback_migrate_page() is not suitable. As starter we could kill the automatic assignment of fallback_migrate_page() and non-buffer_head filesystems need to figure out whether fallback_migrate_page() is suitable or not. UBIFS found out the hard way. ;-\ MM folks, do we have a way to force page migration? Maybe we can create a generic stress test. Thanks, //richard -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>