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charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jan 6, 2021 at 3:07 AM Kirill Tkhai wrote: > > On 06.01.2021 01:58, Yang Shi wrote: > > Currently the number of deferred objects are per shrinker, but some slabs, for example, > > vfs inode/dentry cache are per memcg, this would result in poor isolation among memcgs. > > > > The deferred objects typically are generated by __GFP_NOFS allocations, one memcg with > > excessive __GFP_NOFS allocations may blow up deferred objects, then other innocent memcgs > > may suffer from over shrink, excessive reclaim latency, etc. > > > > For example, two workloads run in memcgA and memcgB respectively, workload in B is vfs > > heavy workload. Workload in A generates excessive deferred objects, then B's vfs cache > > might be hit heavily (drop half of caches) by B's limit reclaim or global reclaim. > > > > We observed this hit in our production environment which was running vfs heavy workload > > shown as the below tracing log: > > > > <...>-409454 [016] .... 28286961.747146: mm_shrink_slab_start: super_cache_scan+0x0/0x1a0 ffff9a83046f3458: > > nid: 1 objects to shrink 3641681686040 gfp_flags GFP_HIGHUSER_MOVABLE|__GFP_ZERO pgs_scanned 1 lru_pgs 15721 > > cache items 246404277 delta 31345 total_scan 123202138 > > <...>-409454 [022] .... 28287105.928018: mm_shrink_slab_end: super_cache_scan+0x0/0x1a0 ffff9a83046f3458: > > nid: 1 unused scan count 3641681686040 new scan count 3641798379189 total_scan 602 > > last shrinker return val 123186855 > > > > The vfs cache and page cache ration was 10:1 on this machine, and half of caches were dropped. > > This also resulted in significant amount of page caches were dropped due to inodes eviction. > > > > Make nr_deferred per memcg for memcg aware shrinkers would solve the unfairness and bring > > better isolation. > > > > When memcg is not enabled (!CONFIG_MEMCG or memcg disabled), the shrinker's nr_deferred > > would be used. And non memcg aware shrinkers use shrinker's nr_deferred all the time. > > > > Signed-off-by: Yang Shi > > --- > > include/linux/memcontrol.h | 7 +++--- > > mm/vmscan.c | 49 +++++++++++++++++++++++++------------- > > 2 files changed, 37 insertions(+), 19 deletions(-) > > > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > > index e05bbe8277cc..5599082df623 100644 > > --- a/include/linux/memcontrol.h > > +++ b/include/linux/memcontrol.h > > @@ -93,12 +93,13 @@ struct lruvec_stat { > > }; > > > > /* > > - * Bitmap of shrinker::id corresponding to memcg-aware shrinkers, > > - * which have elements charged to this memcg. > > + * Bitmap and deferred work of shrinker::id corresponding to memcg-aware > > + * shrinkers, which have elements charged to this memcg. > > */ > > struct memcg_shrinker_info { > > struct rcu_head rcu; > > - unsigned long map[]; > > + unsigned long *map; > > + atomic_long_t *nr_deferred; > > }; > > > > /* > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 0033659abf9e..72259253e414 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -193,10 +193,12 @@ static void memcg_free_shrinker_info_rcu(struct rcu_head *head) > > } > > > > static int memcg_expand_one_shrinker_info(struct mem_cgroup *memcg, > > - int size, int old_size) > > + int m_size, int d_size, > > + int old_m_size, int old_d_size) > > { > > struct memcg_shrinker_info *new, *old; > > int nid; > > + int size = m_size + d_size; > > > > for_each_node(nid) { > > old = rcu_dereference_protected( > > @@ -209,9 +211,18 @@ static int memcg_expand_one_shrinker_info(struct mem_cgroup *memcg, > > if (!new) > > return -ENOMEM; > > > > - /* Set all old bits, clear all new bits */ > > - memset(new->map, (int)0xff, old_size); > > - memset((void *)new->map + old_size, 0, size - old_size); > > + new->map = (unsigned long *)((unsigned long)new + sizeof(*new)); > > + new->nr_deferred = (atomic_long_t *)((unsigned long)new + > > + sizeof(*new) + m_size); > > Can't we write this more compact? > > new->map = (unsigned long *)(new + 1); > new->nr_deferred = (atomic_long_t)(new->map + 1); By relooking this, the second line looks wrong. The layout should be: ---------------------------- | struct shrinker_info | ----------------------------- | map array | ----------------------------- | nr_deferred array | ------------------------------ new->map is the pointer to map array, its type is "unsigned long *", so "new->map + 1" should point to the next 32 bytes, but the map array may occupy more than one "unsigned long", this would corrupt the arrays. I think we could use "new->map + (shrinker_nr_max / BITS_PER_LONG) + 1" > > > + > > + /* map: set all old bits, clear all new bits */ > > + memset(new->map, (int)0xff, old_m_size); > > + memset((void *)new->map + old_m_size, 0, m_size - old_m_size); > > + /* nr_deferred: copy old values, clear all new values */ > > + memcpy((void *)new->nr_deferred, (void *)old->nr_deferred, > > + old_d_size); > > Why not > memcpy(new->nr_deferred, old->nr_deferred, old_d_size); > ? > > > + memset((void *)new->nr_deferred + old_d_size, 0, > > + d_size - old_d_size); > > > > rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, new); > > call_rcu(&old->rcu, memcg_free_shrinker_info_rcu); > > @@ -226,9 +237,6 @@ void memcg_free_shrinker_info(struct mem_cgroup *memcg) > > struct memcg_shrinker_info *info; > > int nid; > > > > - if (mem_cgroup_is_root(memcg)) > > - return; > > - > > for_each_node(nid) { > > pn = mem_cgroup_nodeinfo(memcg, nid); > > info = rcu_dereference_protected(pn->shrinker_info, true); > > @@ -242,12 +250,13 @@ int memcg_alloc_shrinker_info(struct mem_cgroup *memcg) > > { > > struct memcg_shrinker_info *info; > > int nid, size, ret = 0; > > - > > - if (mem_cgroup_is_root(memcg)) > > - return 0; > > + int m_size, d_size = 0; > > > > down_read(&shrinker_rwsem); > > - size = DIV_ROUND_UP(shrinker_nr_max, BITS_PER_LONG) * sizeof(unsigned long); > > + m_size = DIV_ROUND_UP(shrinker_nr_max, BITS_PER_LONG) * sizeof(unsigned long); > > + d_size = shrinker_nr_max * sizeof(atomic_long_t); > > + size = m_size + d_size; > > + > > for_each_node(nid) { > > info = kvzalloc(sizeof(*info) + size, GFP_KERNEL); > > if (!info) { > > @@ -255,6 +264,9 @@ int memcg_alloc_shrinker_info(struct mem_cgroup *memcg) > > ret = -ENOMEM; > > break; > > } > > + info->map = (unsigned long *)((unsigned long)info + sizeof(*info)); > > + info->nr_deferred = (atomic_long_t *)((unsigned long)info + > > + sizeof(*info) + m_size); > > rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info); > > } > > up_read(&shrinker_rwsem); > > @@ -265,10 +277,16 @@ int memcg_alloc_shrinker_info(struct mem_cgroup *memcg) > > static int memcg_expand_shrinker_info(int new_id) > > { > > int size, old_size, ret = 0; > > + int m_size, d_size = 0; > > + int old_m_size, old_d_size = 0; > > struct mem_cgroup *memcg; > > > > - size = DIV_ROUND_UP(new_id + 1, BITS_PER_LONG) * sizeof(unsigned long); > > - old_size = DIV_ROUND_UP(shrinker_nr_max, BITS_PER_LONG) * sizeof(unsigned long); > > + m_size = DIV_ROUND_UP(new_id + 1, BITS_PER_LONG) * sizeof(unsigned long); > > + d_size = (new_id + 1) * sizeof(atomic_long_t); > > + size = m_size + d_size; > > + old_m_size = DIV_ROUND_UP(shrinker_nr_max, BITS_PER_LONG) * sizeof(unsigned long); > > + old_d_size = shrinker_nr_max * sizeof(atomic_long_t); > > + old_size = old_m_size + old_d_size; > > if (size <= old_size) > > return 0; > > This replication of patch [4/11] looks awkwardly. Please, try to incorporate > the same changes to nr_deferred as I requested for shrinker_map in [4/11]. > > > > > @@ -277,9 +295,8 @@ static int memcg_expand_shrinker_info(int new_id) > > > > memcg = mem_cgroup_iter(NULL, NULL, NULL); > > do { > > - if (mem_cgroup_is_root(memcg)) > > - continue; > > - ret = memcg_expand_one_shrinker_info(memcg, size, old_size); > > + ret = memcg_expand_one_shrinker_info(memcg, m_size, d_size, > > + old_m_size, old_d_size); > > if (ret) { > > mem_cgroup_iter_break(NULL, memcg); > > goto out; > > > >