Re: [PATCH 7/8] mm: vmscan: split shrink_node() into node part and memcgs part

[Roman Gushchin <guro@fb.com>]

On Tue, Oct 22, 2019 at 10:48:02AM -0400, Johannes Weiner wrote:
> This function is getting long and unwieldy, split out the memcg bits.
> 
> The updated shrink_node() handles the generic (node) reclaim aspects:
>   - global vmpressure notifications
>   - writeback and congestion throttling
>   - reclaim/compaction management
>   - kswapd giving up on unreclaimable nodes
> 
> It then calls a new shrink_node_memcgs() which handles cgroup specifics:
>   - the cgroup tree traversal
>   - memory.low considerations
>   - per-cgroup slab shrinking callbacks
>   - per-cgroup vmpressure notifications
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  mm/vmscan.c | 28 ++++++++++++++++++----------
>  1 file changed, 18 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index db073b40c432..65baa89740dd 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2722,18 +2722,10 @@ static bool pgdat_memcg_congested(pg_data_t *pgdat, struct mem_cgroup *memcg)
>  		(memcg && memcg_congested(pgdat, memcg));
>  }
>  
> -static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
> +static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
>  {
> -	struct reclaim_state *reclaim_state = current->reclaim_state;
>  	struct mem_cgroup *root = sc->target_mem_cgroup;
> -	unsigned long nr_reclaimed, nr_scanned;
> -	bool reclaimable = false;
>  	struct mem_cgroup *memcg;
> -again:
> -	memset(&sc->nr, 0, sizeof(sc->nr));
> -
> -	nr_reclaimed = sc->nr_reclaimed;
> -	nr_scanned = sc->nr_scanned;
>  
>  	memcg = mem_cgroup_iter(root, NULL, NULL);
>  	do {
> @@ -2786,6 +2778,22 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
>  			   sc->nr_reclaimed - reclaimed);
>  
>  	} while ((memcg = mem_cgroup_iter(root, memcg, NULL)));
> +}
> +
> +static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
> +{
> +	struct reclaim_state *reclaim_state = current->reclaim_state;
> +	struct mem_cgroup *root = sc->target_mem_cgroup;
> +	unsigned long nr_reclaimed, nr_scanned;
> +	bool reclaimable = false;
> +
> +again:
> +	memset(&sc->nr, 0, sizeof(sc->nr));
> +
> +	nr_reclaimed = sc->nr_reclaimed;
> +	nr_scanned = sc->nr_scanned;
> +
> +	shrink_node_memcgs(pgdat, sc);
>  
>  	if (reclaim_state) {
>  		sc->nr_reclaimed += reclaim_state->reclaimed_slab;
> @@ -2793,7 +2801,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
>  	}
>  
>  	/* Record the subtree's reclaim efficiency */
> -	vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
> +	vmpressure(sc->gfp_mask, root, true,

Maybe target? Or target_memcg? The word root is associated with the root cgroup.

Other than root the patch looks good to me:

Reviewed-by: Roman Gushchin <guro@fb.com>