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On 6/21/2017 10:01 PM, Vladimir Davydov wrote: > >> index cddf397..c8ca150 100644 >> --- a/fs/dcache.c >> +++ b/fs/dcache.c >> @@ -1133,10 +1133,11 @@ void shrink_dcache_sb(struct super_block *sb) >> LIST_HEAD(dispose); >> >> freed = list_lru_walk(&sb->s_dentry_lru, >> - dentry_lru_isolate_shrink, &dispose, UINT_MAX); >> + dentry_lru_isolate_shrink, &dispose, 1024); >> >> this_cpu_sub(nr_dentry_unused, freed); >> shrink_dentry_list(&dispose); >> + cond_resched(); >> } while (freed > 0); > In an extreme case, a single invocation of list_lru_walk() can skip all > 1024 dentries, in which case 'freed' will be 0 forcing us to break the > loop prematurely. I think we should loop until there's at least one > dentry left on the LRU, i.e. > > while (list_lru_count(&sb->s_dentry_lru) > 0) > > However, even that wouldn't be quite correct, because list_lru_count() > iterates over all memory cgroups to sum list_lru_one->nr_items, which > can race with memcg offlining code migrating dentries off a dead cgroup > (see memcg_drain_all_list_lrus()). So it looks like to make this check > race-free, we need to account the number of entries on the LRU not only > per memcg, but also per node, i.e. add list_lru_node->nr_items. > Fortunately, list_lru entries can't be migrated between NUMA nodes. It looks like list_lru_count() is iterating per node before iterating over all memory cgroups as below -
unsigned long list_lru_count_node(struct list_lru *lru, int nid) { long count = 0; int memcg_idx;
count += __list_lru_count_one(lru, nid, -1); if (list_lru_memcg_aware(lru)) { for_each_memcg_cache_index(memcg_idx) count += __list_lru_count_one(lru, nid, memcg_idx); } return count; }
The first call to __list_lru_count_one() is iterating all the items per node i.e, nlru->lru->nr_items. Is my understanding correct? If not, could you please clarify on how to get the lru items per node?
-- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
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