On Sat, Jan 14, 2023 at 6:51 AM Vlastimil Babka vbabka@suse.cz 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@kernel.org/ Fixes: 7efc3b726103 ("mm/compaction: fix set skip in fast_find_migrateblock") Cc: stable@vger.kernel.org
Oops, forgot:
Signed-off-by: Vlastimil Babka vbabka@suse.cz
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@gmail.com
I'll report back if QEMU freezes the system again.