On 13.05.2018 08:15, Vladimir Davydov wrote: > On Thu, May 10, 2018 at 12:52:18PM +0300, Kirill Tkhai wrote: >> The patch introduces shrinker::id number, which is used to enumerate >> memcg-aware shrinkers. The number start from 0, and the code tries >> to maintain it as small as possible. >> >> This will be used as to represent a memcg-aware shrinkers in memcg >> shrinkers map. >> >> Since all memcg-aware shrinkers are based on list_lru, which is per-memcg >> in case of !SLOB only, the new functionality will be under MEMCG && !SLOB >> ifdef (symlinked to CONFIG_MEMCG_SHRINKER). > > Using MEMCG && !SLOB instead of introducing a new config option was done > deliberately, see: > > http://lkml.kernel.org/r/20151210202244.GA4809@xxxxxxxxxxx > > I guess, this doesn't work well any more, as there are more and more > parts depending on kmem accounting, like shrinkers. If you really want > to introduce a new option, I think you should call it CONFIG_MEMCG_KMEM > and use it consistently throughout the code instead of MEMCG && !SLOB. > And this should be done in a separate patch. What do you mean under "consistently throughout the code"? Should I replace all MEMCG && !SLOB with CONFIG_MEMCG_KMEM over existing code? >> diff --git a/fs/super.c b/fs/super.c >> index 122c402049a2..16c153d2f4f1 100644 >> --- a/fs/super.c >> +++ b/fs/super.c >> @@ -248,6 +248,9 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags, >> s->s_time_gran = 1000000000; >> s->cleancache_poolid = CLEANCACHE_NO_POOL; >> >> +#ifdef CONFIG_MEMCG_SHRINKER >> + s->s_shrink.id = -1; >> +#endif > > No point doing that - you are going to overwrite the id anyway in > prealloc_shrinker(). Not so, this is done deliberately. alloc_super() has the only "fail" label, and it handles all the allocation errors there. The patch just behaves in the same style. It sets "-1" to make destroy_unused_super() able to differ the cases, when shrinker is really initialized, and when it's not. If you don't like this, I can move "s->s_shrink.id = -1;" into prealloc_memcg_shrinker() instead of this. >> s->s_shrink.seeks = DEFAULT_SEEKS; >> s->s_shrink.scan_objects = super_cache_scan; >> s->s_shrink.count_objects = super_cache_count; > >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 10c8a38c5eef..d691beac1048 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -169,6 +169,47 @@ unsigned long vm_total_pages; >> static LIST_HEAD(shrinker_list); >> static DECLARE_RWSEM(shrinker_rwsem); >> >> +#ifdef CONFIG_MEMCG_SHRINKER >> +static DEFINE_IDR(shrinker_idr); >> + >> +static int prealloc_memcg_shrinker(struct shrinker *shrinker) >> +{ >> + int id, ret; >> + >> + down_write(&shrinker_rwsem); >> + ret = id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL); >> + if (ret < 0) >> + goto unlock; >> + shrinker->id = id; >> + ret = 0; >> +unlock: >> + up_write(&shrinker_rwsem); >> + return ret; >> +} >> + >> +static void del_memcg_shrinker(struct shrinker *shrinker) > > Nit: IMO unregister_memcg_shrinker() would be a better name as it > matches unregister_shrinker(), just like prealloc_memcg_shrinker() > matches prealloc_shrinker(). > >> +{ >> + int id = shrinker->id; >> + > >> + if (id < 0) >> + return; > > Nit: I think this should be BUG_ON(id >= 0) as this function is only > called for memcg-aware shrinkers AFAICS. See comment to alloc_super(). >> + >> + down_write(&shrinker_rwsem); >> + idr_remove(&shrinker_idr, id); >> + up_write(&shrinker_rwsem); >> + shrinker->id = -1; >> +} Kirill
