On Mon, 22 Aug 2011 14:17:21 +0300
Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> wrote:
> Shrinker function can returns -1, it means it cannot do anything without a risk of deadlock.
> For example prune_super() do this if it cannot grab superblock refrence, even if nr_to_scan=0.
> Currenly we interpret this like ULONG_MAX size shrinker, evaluate total_scan according this,
> and next time this shrinker can get really big pressure. Let's skip such shrinkers instead.
Yes, that looks like a significant oversight.
> Also make total_scan signed, otherwise check (total_scan < 0) below never works.
Hopefully a smaller oversight.
> ---
> mm/vmscan.c | 9 ++++++---
> 1 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 29b3612..f174561 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -248,14 +248,18 @@ unsigned long shrink_slab(struct shrink_control *shrink,
>
> list_for_each_entry(shrinker, &shrinker_list, list) {
> unsigned long long delta;
> - unsigned long total_scan;
> - unsigned long max_pass;
> + long total_scan;
> + long max_pass;
> int shrink_ret = 0;
> long nr;
> long new_nr;
> long batch_size = shrinker->batch ? shrinker->batch
> : SHRINK_BATCH;
>
> + max_pass = do_shrinker_shrink(shrinker, shrink, 0);
> + if (max_pass <= 0)
> + continue;
> +
> /*
> * copy the current shrinker scan count into a local variable
> * and zero it so that other concurrent shrinker invocations
> @@ -266,7 +270,6 @@ unsigned long shrink_slab(struct shrink_control *shrink,
> } while (cmpxchg(&shrinker->nr, nr, 0) != nr);
>
> total_scan = nr;
> - max_pass = do_shrinker_shrink(shrinker, shrink, 0);
> delta = (4 * nr_pages_scanned) / shrinker->seeks;
> delta *= max_pass;
> do_div(delta, lru_pages + 1);
Why was the shrinker call moved to before the alteration of shrinker->nr?
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