On Wed, May 23, 2018 at 11:50:41AM -0700, Tejun Heo wrote: > Currently an attempt to set swap.max into a value lower than the > actual swap usage fails, which causes configuration problems as > there's no way of lowering the configuration below the current usage > short of turning off swap entirely. This makes swap.max difficult to > use and allows delegatees to lock the delegator out of reducing swap > allocation. > > This patch updates swap_max_write() so that the limit can be lowered > below the current usage. It doesn't implement active reclaiming of > swap entries for the following reasons. > > * mem_cgroup_swap_full() already tells the swap machinary to > aggressively reclaim swap entries if the usage is above 50% of > limit, so simply lowering the limit automatically triggers gradual > reclaim. > > * Forcing back swapped out pages is likely to heavily impact the > workload and mess up the working set. Given that swap usually is a > lot less valuable and less scarce, letting the existing usage > dissipate over time through the above gradual reclaim and as they're > falted back in is likely the better behavior. > > Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> > Acked-by: Roman Gushchin <guro@xxxxxx> > Acked-by: Rik van Riel <riel@xxxxxxxxxxx> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > Cc: Shaohua Li <shli@xxxxxx> > Cc: linux-kernel@xxxxxxxxxxxxxxx > Cc: linux-mm@xxxxxxxxx > Cc: cgroups@xxxxxxxxxxxxxxx Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
