On Sat, Jan 14, 2023 at 6:51 AM Vlastimil Babka <vbabka@xxxxxxx> wrote: > > On 1/13/23 18:33, Vlastimil Babka wrote: > > This reverts commit 7efc3b7261030da79001c00d92bc3392fd6c664c. > > > > We have got openSUSE reports (Link 1) for 6.1 kernel with khugepaged > > stalling CPU for long periods of time. Investigation of tracepoint data > > shows that compaction is stuck in repeating fast_find_migrateblock() > > based migrate page isolation, and then fails to migrate all isolated > > pages. Commit 7efc3b726103 ("mm/compaction: fix set skip in > > fast_find_migrateblock") was suspected as it was merged in 6.1 and in > > theory can indeed remove a termination condition for > > fast_find_migrateblock() under certain conditions, as it removes a place > > that always marks a scanned pageblock from being re-scanned. There are > > other such places, but those can be skipped under certain conditions, > > which seems to match the tracepoint data. > > > > Testing of revert also appears to have resolved the issue, thus revert > > the commit until a more robust solution for the original problem is > > developed. > > > > It's also likely this will fix qemu stalls with 6.1 kernel reported in > > Link 2, but that is not yet confirmed. > > > > Link: https://bugzilla.suse.com/show_bug.cgi?id=1206848 > > Link: https://lore.kernel.org/kvm/b8017e09-f336-3035-8344-c549086c2340@xxxxxxxxxx/ > > Fixes: 7efc3b726103 ("mm/compaction: fix set skip in fast_find_migrateblock") > > Cc: <stable@xxxxxxxxxxxxxxx> > > Oops, forgot: > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> > > > --- > > mm/compaction.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/mm/compaction.c b/mm/compaction.c > > index ca1603524bbe..8238e83385a7 100644 > > --- a/mm/compaction.c > > +++ b/mm/compaction.c > > @@ -1839,6 +1839,7 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc) > > pfn = cc->zone->zone_start_pfn; > > cc->fast_search_fail = 0; > > found_block = true; > > + set_pageblock_skip(freepage); > > break; > > } > > } > Vlastimil, Thank you so much for looking into this. I've been daily driving it for the past half day and it seems to have fixed my QEMU issues. Of course, I don't have exactly a test suite for this but I've tried everything and I can't get any of the original problems to show up. That being said, Tested-by: Pedro Falcato <pedro.falcato@xxxxxxxxx> I'll report back if QEMU freezes the system again. -- Pedro