On Fri 28-04-23 18:08:46, Yajun Deng wrote:
> When migration failure in do_migrate_range() and then the
> scan_movable_pages() will most likely return the same movable pfn.
> In this case, there is no condition to bail out, they will
> always run like this:
>
> ...
> [878020.623959] migrating pfn 1727813 failed ret:1
> [878020.623960] page:00000000faa9673c refcount:3 mapcount:0 mapping:00000000144ccd79 index:0x14280025 pfn:0x1727813
> [878020.623962] memcg:ffffa0ff82d5a000
> [878020.623962] aops:def_blk_aops ino:fd00001
> [878020.623964] flags: 0x17ffffc000206a(referenced|dirty|active|workingset|private|node=0|zone=2|lastcpupid=0x1fffff)
> [878020.623966] raw: 0017ffffc000206a ffffb0d14f50fbd8 ffffb0d14f50fbd8 ffffa0ff9c155018
> [878020.623967] raw: 0000000014280025 ffffa10327d702d8 00000003ffffffff ffffa0ff82d5a000
> [878020.623968] page dumped because: migration failure
> [878020.626196] migrating pfn 1727813 failed ret:1
> [878020.626198] page:00000000faa9673c refcount:3 mapcount:0 mapping:00000000144ccd79 index:0x14280025 pfn:0x1727813
> [878020.626200] memcg:ffffa0ff82d5a000
> [878020.626200] aops:def_blk_aops ino:fd00001
> [878020.626202] flags: 0x17ffffc000206a(referenced|dirty|active|workingset|private|node=0|zone=2|lastcpupid=0x1fffff)
> [878020.626204] raw: 0017ffffc000206a ffffb0d14f50fbd8 ffffb0d14f50fbd8 ffffa0ff9c155018
> [878020.626205] raw: 0000000014280025 ffffa10327d702d8 00000003ffffffff ffffa0ff82d5a000
> [878020.626206] page dumped because: migration failure
> ...
>
> Bail out when migration failures reach 3 times.
>
> Fixes: bb8965bd82fd ("mm, memory_hotplug: deobfuscate migration part of offlining")
> Signed-off-by: Yajun Deng <yajun.deng@xxxxxxxxx>
Any hard coded failure retry limit will lead to premature failures. Have
a look at 72b39cfc4d75 ("mm, memory_hotplug: do not fail offlining too
early"). A proper way to deal with this is to implement termination from
the userspace (e.g. timeout $TIMEOUT /bin/echo 0 > $PATH_TO_MEM/online)
Nacked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> mm/memory_hotplug.c | 19 ++++++++++++++-----
> 1 file changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 8e0fa209d533..72dd385b8892 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1800,11 +1800,12 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
> struct zone *zone, struct memory_group *group)
> {
> const unsigned long end_pfn = start_pfn + nr_pages;
> - unsigned long pfn, system_ram_pages = 0;
> + unsigned long pfn, tmp_pfn, system_ram_pages = 0;
> const int node = zone_to_nid(zone);
> unsigned long flags;
> struct memory_notify arg;
> char *reason;
> + int count = 0;
> int ret;
>
> /*
> @@ -1887,12 +1888,20 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
>
> cond_resched();
>
> + tmp_pfn = pfn;
> ret = scan_movable_pages(pfn, end_pfn, &pfn);
> if (!ret) {
> - /*
> - * TODO: fatal migration failures should bail
> - * out
> - */
> + if (pfn == tmp_pfn)
> + count++;
> + else
> + count = 0;
> +
> + if (unlikely(count == 3)) {
> + ret = -EBUSY;
> + reason = "migration failure";
> + goto failed_removal_isolated;
> + }
> +
> do_migrate_range(pfn, end_pfn);
> }
> } while (!ret);
> --
> 2.25.1
--
Michal Hocko
SUSE Labs
