Re: [PATCH v7 15/16] mm/mglru: Make swappiness=1 file reclaim more aggressive

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] mm/mglru: missing sc.priority init for lru_gen_balance_scan()
  via debugfs
--

commit cf50aabb1ef5db31c58a09226fe4dbb55149d981
Author: Barry Song (Xiaomi) <baohua@kernel.org>

mm/mglru: Make swappiness=1 file reclaim more aggressive

This commit sets anon_factor to 0 in lru_gen_balance_scan() when swappiness
is 1 and sc->priority is above DEF_PRIORITY / 2, making file reclaim more
aggressive at normal reclaim priorities.

> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a92b14190d733..f36e9a379b62a 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -4946,7 +4946,11 @@ static void lru_gen_balance_scan(struct lruvec *lruvec, struct scan_control *sc,
>  	anon_weight = nr[LRU_GEN_ANON] + nr[LRU_GEN_FILE] / size_bias;
>  	file_weight = nr[LRU_GEN_FILE] + nr[LRU_GEN_ANON] / size_bias;
>  
> -	anon_factor = (u64)swappiness * refault_rate[LRU_GEN_FILE] * anon_weight;
> +	if (swappiness == MIN_SWAPPINESS + 1)
> +		anon_factor = sc->priority <= DEF_PRIORITY / 2 ?
> +			      refault_rate[LRU_GEN_FILE] * anon_weight : 0;
> +	else
> +		anon_factor = (u64)swappiness * refault_rate[LRU_GEN_FILE] * anon_weight;

[Severity: Low]
Does the sc->priority <= DEF_PRIORITY / 2 check always evaluate to true when
lru_gen_balance_scan() is called from the debugfs eviction path
(lru_gen_seq_write() -> run_cmd() -> run_eviction())?

lru_gen_seq_write() allocates sc on the stack without initializing
.priority, so sc.priority is 0 and anon_factor is never zeroed out for
swappiness=1 during debugfs proactive eviction.  Should lru_gen_seq_write()
initialize .priority = DEF_PRIORITY in sc (as commit "mm/mglru: balance anon
and file scan budget by refault rate" noted in its commit message)?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111232603.9934-1-baohua@kernel.org?part=15