On Tue, Nov 23, 2021 at 11:09 AM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
>
> The deferred THPs are split on memory pressure through shrinker
> callback and splitting of THP during reclaim can fail for several
> reasons like unable to lock the THP, under writeback or unexpected
> number of pins on the THP. Such pages are put back on the deferred split
> list for consideration later. However kernel does not update the
> deferred queue size on putting back the pages whose split was failed.
> This patch fixes that.
>
> Without this patch the split_queue_len can underflow. Shrinker will
> always get that there are some THPs to split even if there are not and
> waste some cpu to scan the empty list.
>
> Fixes: 364c1eebe453 ("mm: thp: extract split_queue_* into a struct")
> Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> ---
> Changes since v1:
> - updated commit message
> - incorporated Yang Shi's suggestion
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
>
> mm/huge_memory.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index e5483347291c..d393028681e2 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2809,7 +2809,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
> unsigned long flags;
> LIST_HEAD(list), *pos, *next;
> struct page *page;
> - int split = 0;
> + unsigned long split = 0;
>
> #ifdef CONFIG_MEMCG
> if (sc->memcg)
> @@ -2847,6 +2847,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
>
> spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
> list_splice_tail(&list, &ds_queue->split_queue);
> + ds_queue->split_queue_len -= split;
> spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
>
> /*
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>
