Re: [patch v2] mm, vmscan: avoid thrashing anon lru when free + file is low

[David Rientjes]

On Fri, 2 Jun 2017, Andrew Morton wrote:

> On Mon, 1 May 2017 14:34:21 -0700 (PDT) David Rientjes <rientjes@xxxxxxxxxx> wrote:
> 
> > The purpose of the code that commit 623762517e23 ("revert 'mm: vmscan: do
> > not swap anon pages just because free+file is low'") reintroduces is to
> > prefer swapping anonymous memory rather than trashing the file lru.
> > 
> > If the anonymous inactive lru for the set of eligible zones is considered
> > low, however, or the length of the list for the given reclaim priority
> > does not allow for effective anonymous-only reclaiming, then avoid
> > forcing SCAN_ANON.  Forcing SCAN_ANON will end up thrashing the small
> > list and leave unreclaimed memory on the file lrus.
> > 
> > If the inactive list is insufficient, fallback to balanced reclaim so the
> > file lru doesn't remain untouched.
> > 
> 
> --- a/mm/vmscan.c~mm-vmscan-avoid-thrashing-anon-lru-when-free-file-is-low-fix
> +++ a/mm/vmscan.c
> @@ -2233,7 +2233,7 @@ static void get_scan_count(struct lruvec
>  			 * anonymous pages on the LRU in eligible zones.
>  			 * Otherwise, the small LRU gets thrashed.
>  			 */
> -			if (!inactive_list_is_low(lruvec, false, sc, false) &&
> +			if (!inactive_list_is_low(lruvec, false, memcg, sc, false) &&
>  			    lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, sc->reclaim_idx)
>  					>> sc->priority) {
>  				scan_balance = SCAN_ANON;
> 
> Worried.  Did you send the correct version?
> 

The patch was written before commit 2a2e48854d70 ("mm: vmscan: fix 
IO/refault regression in cache workingset transition") was merged and 
changed inactive_list_is_low().

Your rebase looks good.  It could have used NULL instead of memcg since 
this is only for global_reclaim() and memcg will always be NULL here, but 
that's just personal preference.