Re: [PATCH] mm: thp: update split_queue_len correctly

[Shakeel Butt]

On Tue, Nov 23, 2021 at 9:47 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.

I forgot to add the user visible impact.

"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."