| Message ID | 153063066653.1818.976035462801487910.stgit@localhost.localdomain (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, 03 Jul 2018 18:11:06 +0300 Kirill Tkhai <ktkhai@virtuozzo.com> wrote: > Using the preparations made in previous patches, in case of memcg > shrink, we may avoid shrinkers, which are not set in memcg's shrinkers > bitmap. To do that, we separate iterations over memcg-aware and > !memcg-aware shrinkers, and memcg-aware shrinkers are chosen > via for_each_set_bit() from the bitmap. In case of big nodes, > having many isolated environments, this gives significant > performance growth. See next patches for the details. > > Note, that the patch does not respect to empty memcg shrinkers, > since we never clear the bitmap bits after we set it once. > Their shrinkers will be called again, with no shrinked objects > as result. This functionality is provided by next patches. > > ... > > @@ -541,6 +555,67 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, > return freed; > } > > +#ifdef CONFIG_MEMCG_KMEM > +static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, > + struct mem_cgroup *memcg, int priority) > +{ > + struct memcg_shrinker_map *map; > + unsigned long freed = 0; > + int ret, i; > + > + if (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)) > + return 0; > + > + if (!down_read_trylock(&shrinker_rwsem)) > + return 0; Why trylock? Presumably some other code path is known to hold the lock for long periods? Dunno. Comment it, please. > + /* > + * 1) Caller passes only alive memcg, so map can't be NULL. > + * 2) shrinker_rwsem protects from maps expanding. > + */ > + map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map, > + true); > + BUG_ON(!map); > + > + for_each_set_bit(i, map->map, shrinker_nr_max) { > + struct shrink_control sc = { > + .gfp_mask = gfp_mask, > + .nid = nid, > + .memcg = memcg, > + }; > + struct shrinker *shrinker; > + > + shrinker = idr_find(&shrinker_idr, i); > + if (unlikely(!shrinker)) { > + clear_bit(i, map->map); > + continue; > + } > + BUG_ON(!(shrinker->flags & SHRINKER_MEMCG_AWARE)); Fair enough as a development-time sanity check but we shouldn't need this in production code. Or make it VM_BUG_ON(), at least. > + /* See comment in prealloc_shrinker() */ > + if (unlikely(list_empty(&shrinker->list))) > + continue; > + > + ret = do_shrink_slab(&sc, shrinker, priority); > + freed += ret; > + > + if (rwsem_is_contended(&shrinker_rwsem)) { > + freed = freed ? : 1; > + break; > + } > + } > + > + up_read(&shrinker_rwsem); > + return freed; > +}
On 03.07.2018 23:58, Andrew Morton wrote: > On Tue, 03 Jul 2018 18:11:06 +0300 Kirill Tkhai <ktkhai@virtuozzo.com> wrote: > >> Using the preparations made in previous patches, in case of memcg >> shrink, we may avoid shrinkers, which are not set in memcg's shrinkers >> bitmap. To do that, we separate iterations over memcg-aware and >> !memcg-aware shrinkers, and memcg-aware shrinkers are chosen >> via for_each_set_bit() from the bitmap. In case of big nodes, >> having many isolated environments, this gives significant >> performance growth. See next patches for the details. >> >> Note, that the patch does not respect to empty memcg shrinkers, >> since we never clear the bitmap bits after we set it once. >> Their shrinkers will be called again, with no shrinked objects >> as result. This functionality is provided by next patches. >> >> ... >> >> @@ -541,6 +555,67 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, >> return freed; >> } >> >> +#ifdef CONFIG_MEMCG_KMEM >> +static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, >> + struct mem_cgroup *memcg, int priority) >> +{ >> + struct memcg_shrinker_map *map; >> + unsigned long freed = 0; >> + int ret, i; >> + >> + if (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)) >> + return 0; >> + >> + if (!down_read_trylock(&shrinker_rwsem)) >> + return 0; > > Why trylock? Presumably some other code path is known to hold the lock > for long periods? Dunno. We take shrinker_rwsem in prealloc_memcg_shrinker() and do memory allocation there. It may result in reclaim under shrinker_rwsem write locked, so we use down_read_trylock() to avoid deadlocks. The first versions of the patchset contained different lock for this function, but it has gone in the process of review. >Comment it, please. OK >> + /* >> + * 1) Caller passes only alive memcg, so map can't be NULL. >> + * 2) shrinker_rwsem protects from maps expanding. >> + */ >> + map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map, >> + true); >> + BUG_ON(!map); >> + >> + for_each_set_bit(i, map->map, shrinker_nr_max) { >> + struct shrink_control sc = { >> + .gfp_mask = gfp_mask, >> + .nid = nid, >> + .memcg = memcg, >> + }; >> + struct shrinker *shrinker; >> + >> + shrinker = idr_find(&shrinker_idr, i); >> + if (unlikely(!shrinker)) { >> + clear_bit(i, map->map); >> + continue; >> + } >> + BUG_ON(!(shrinker->flags & SHRINKER_MEMCG_AWARE)); > > Fair enough as a development-time sanity check but we shouldn't need > this in production code. Or make it VM_BUG_ON(), at least. OK >> + /* See comment in prealloc_shrinker() */ >> + if (unlikely(list_empty(&shrinker->list))) >> + continue; >> + >> + ret = do_shrink_slab(&sc, shrinker, priority); >> + freed += ret; >> + >> + if (rwsem_is_contended(&shrinker_rwsem)) { >> + freed = freed ? : 1; >> + break; >> + } >> + } >> + >> + up_read(&shrinker_rwsem); >> + return freed; >> +} >
diff --git a/mm/vmscan.c b/mm/vmscan.c index d8b1958c751d..d4c40ed9ec5d 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -367,6 +367,20 @@ int prealloc_shrinker(struct shrinker *shrinker) goto free_deferred; } + /* + * There is a window between prealloc_shrinker() + * and register_shrinker_prepared(). We don't want + * to clear bit of a shrinker in such the state + * in shrink_slab_memcg(), since this will impose + * restrictions on a code registering a shrinker + * (they would have to guarantee, their LRU lists + * are empty till shrinker is completely registered). + * So, we differ the situation, when 1)a shrinker + * is semi-registered (id is assigned, but it has + * not yet linked to shrinker_list) and 2)shrinker + * is not registered (id is not assigned). + */ + INIT_LIST_HEAD(&shrinker->list); return 0; free_deferred: @@ -541,6 +555,67 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl, return freed; } +#ifdef CONFIG_MEMCG_KMEM +static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, + struct mem_cgroup *memcg, int priority) +{ + struct memcg_shrinker_map *map; + unsigned long freed = 0; + int ret, i; + + if (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)) + return 0; + + if (!down_read_trylock(&shrinker_rwsem)) + return 0; + + /* + * 1) Caller passes only alive memcg, so map can't be NULL. + * 2) shrinker_rwsem protects from maps expanding. + */ + map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map, + true); + BUG_ON(!map); + + for_each_set_bit(i, map->map, shrinker_nr_max) { + struct shrink_control sc = { + .gfp_mask = gfp_mask, + .nid = nid, + .memcg = memcg, + }; + struct shrinker *shrinker; + + shrinker = idr_find(&shrinker_idr, i); + if (unlikely(!shrinker)) { + clear_bit(i, map->map); + continue; + } + BUG_ON(!(shrinker->flags & SHRINKER_MEMCG_AWARE)); + + /* See comment in prealloc_shrinker() */ + if (unlikely(list_empty(&shrinker->list))) + continue; + + ret = do_shrink_slab(&sc, shrinker, priority); + freed += ret; + + if (rwsem_is_contended(&shrinker_rwsem)) { + freed = freed ? : 1; + break; + } + } + + up_read(&shrinker_rwsem); + return freed; +} +#else /* CONFIG_MEMCG_KMEM */ +static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, + struct mem_cgroup *memcg, int priority) +{ + return 0; +} +#endif /* CONFIG_MEMCG_KMEM */ + /** * shrink_slab - shrink slab caches * @gfp_mask: allocation context @@ -570,8 +645,8 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, struct shrinker *shrinker; unsigned long freed = 0; - if (memcg && (!memcg_kmem_enabled() || !mem_cgroup_online(memcg))) - return 0; + if (memcg && !mem_cgroup_is_root(memcg)) + return shrink_slab_memcg(gfp_mask, nid, memcg, priority); if (!down_read_trylock(&shrinker_rwsem)) goto out; @@ -583,13 +658,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, .memcg = memcg, }; - /* - * If kernel memory accounting is disabled, we ignore - * SHRINKER_MEMCG_AWARE flag and call all shrinkers - * passing NULL for memcg. - */ - if (memcg_kmem_enabled() && - !!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE)) + if (!!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE)) continue; if (!(shrinker->flags & SHRINKER_NUMA_AWARE))