On Mon 01-03-21 16:09:45, David Hildenbrand wrote:
> The information that some PFNs are busy is:
> a) not helpful for ordinary users: we don't even know *who* called
> alloc_contig_range(). This is certainly not worth a pr_info.*().
> b) not really helpful for debugging: we don't have any details *why*
> these PFNs are busy, and that is what we usually care about.
> c) not complete: there are other cases where we fail alloc_contig_range()
> using different paths that are not getting recorded.
>
> For example, we reach this path once we succeeded in isolating pageblocks,
> but failed to migrate some pages - which can happen easily on
> ZONE_NORMAL (i.e., has_unmovable_pages() is racy) but also on ZONE_MOVABLE
> i.e., we would have to retry longer to migrate).
>
> For example via virtio-mem when unplugging memory, we can create quite
> some noise (especially with ZONE_NORMAL) that is not of interest to
> users - it's expected that some allocations may fail as memory is busy.
>
> Let's just drop that pr_info_ratelimit() and rather implement a dynamic
> debugging mechanism in the future that can give us a better reason why
> alloc_contig_range() failed on specific pages.
>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> mm/page_alloc.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 519a60d5b6f7..efb924fb13e8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8647,8 +8647,6 @@ int alloc_contig_range(unsigned long start, unsigned long end,
>
> /* Make sure the range is really isolated. */
> if (test_pages_isolated(outer_start, end, 0)) {
> - pr_info_ratelimited("%s: [%lx, %lx) PFNs busy\n",
> - __func__, outer_start, end);
> ret = -EBUSY;
> goto done;
> }
> --
> 2.29.2
--
Michal Hocko
SUSE Labs
