On Wed, Mar 10, 2021 at 9:46 AM Yang Shi <shy828301@xxxxxxxxx> wrote: > > The number of deferred objects might get windup to an absurd number, and it > results in clamp of slab objects. It is undesirable for sustaining workingset. > > So shrink deferred objects proportional to priority and cap nr_deferred to twice > of cache items. > > The idea is borrowed from Dave Chinner's patch: > https://lore.kernel.org/linux-xfs/20191031234618.15403-13-david@xxxxxxxxxxxxx/ > > Tested with kernel build and vfs metadata heavy workload in our production > environment, no regression is spotted so far. Did you run both of these workloads in the same cgroup or separate cgroups? > > Signed-off-by: Yang Shi <shy828301@xxxxxxxxx> > --- > mm/vmscan.c | 46 +++++++++++----------------------------------- > 1 file changed, 11 insertions(+), 35 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 9a2dfeaa79f4..6a0a91b23597 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -662,7 +662,6 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, > */ > nr = xchg_nr_deferred(shrinker, shrinkctl); > > - total_scan = nr; > if (shrinker->seeks) { > delta = freeable >> priority; > delta *= 4; > @@ -676,37 +675,9 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, > delta = freeable / 2; > } > > + total_scan = nr >> priority; > total_scan += delta; > - if (total_scan < 0) { > - pr_err("shrink_slab: %pS negative objects to delete nr=%ld\n", > - shrinker->scan_objects, total_scan); > - total_scan = freeable; > - next_deferred = nr; > - } else > - next_deferred = total_scan; > - > - /* > - * We need to avoid excessive windup on filesystem shrinkers > - * due to large numbers of GFP_NOFS allocations causing the > - * shrinkers to return -1 all the time. This results in a large > - * nr being built up so when a shrink that can do some work > - * comes along it empties the entire cache due to nr >>> > - * freeable. This is bad for sustaining a working set in > - * memory. > - * > - * Hence only allow the shrinker to scan the entire cache when > - * a large delta change is calculated directly. > - */ > - if (delta < freeable / 4) > - total_scan = min(total_scan, freeable / 2); > - > - /* > - * Avoid risking looping forever due to too large nr value: > - * never try to free more than twice the estimate number of > - * freeable entries. > - */ > - if (total_scan > freeable * 2) > - total_scan = freeable * 2; > + total_scan = min(total_scan, (2 * freeable)); > > trace_mm_shrink_slab_start(shrinker, shrinkctl, nr, > freeable, delta, total_scan, priority); > @@ -745,10 +716,15 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, > cond_resched(); > } > > - if (next_deferred >= scanned) > - next_deferred -= scanned; > - else > - next_deferred = 0; > + /* > + * The deferred work is increased by any new work (delta) that wasn't > + * done, decreased by old deferred work that was done now. > + * > + * And it is capped to two times of the freeable items. > + */ > + next_deferred = max_t(long, (nr + delta - scanned), 0); > + next_deferred = min(next_deferred, (2 * freeable)); > + > /* > * move the unused scan count back into the shrinker in a > * manner that handles concurrent updates. > -- > 2.26.2 >
