On Tue, Nov 14, 2017 at 10:28:10PM -0800, Shakeel Butt wrote: > On Tue, Nov 14, 2017 at 4:56 PM, Minchan Kim <minc...@kernel.org> wrote: > > On Tue, Nov 14, 2017 at 06:37:42AM +0900, Tetsuo Handa wrote: > >> When shrinker_rwsem was introduced, it was assumed that > >> register_shrinker()/unregister_shrinker() are really unlikely paths > >> which are called during initialization and tear down. But nowadays, > >> register_shrinker()/unregister_shrinker() might be called regularly. > >> This patch prepares for allowing parallel registration/unregistration > >> of shrinkers. > >> > >> Since do_shrink_slab() can reschedule, we cannot protect shrinker_list > >> using one RCU section. But using atomic_inc()/atomic_dec() for each > >> do_shrink_slab() call will not impact so much. > >> > >> This patch uses polling loop with short sleep for unregister_shrinker() > >> rather than wait_on_atomic_t(), for we can save reader's cost (plain > >> atomic_dec() compared to atomic_dec_and_test()), we can expect that > >> do_shrink_slab() of unregistering shrinker likely returns shortly, and > >> we can avoid khungtaskd warnings when do_shrink_slab() of unregistering > >> shrinker unexpectedly took so long. > >> > >> Signed-off-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp> > > > > Before reviewing this patch, can't we solve the problem with more > > simple way? Like this. > > > > Shakeel, What do you think? > > > > Seems simple enough. I will run my test (running fork bomb in one > memcg and separately time a mount operation) and update if numbers > differ significantly.
Thanks. > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 13d711dd8776..cbb624cb9baa 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -498,6 +498,14 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int > > nid, > > sc.nid = 0; > > > > freed += do_shrink_slab(&sc, shrinker, nr_scanned, > > nr_eligible); > > + /* > > + * bail out if someone want to register a new shrinker to > > prevent > > + * long time stall by parallel ongoing shrinking. > > + */ > > + if (rwsem_is_contended(&shrinker_rwsem)) { > > + freed = 1; > > freed = freed ?: 1; Yub.