From: Vladimir Davydov <vdavydov.dev@gmail.com>
To: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: akpm@linux-foundation.org, shakeelb@google.com,
viro@zeniv.linux.org.uk, hannes@cmpxchg.org, mhocko@kernel.org,
tglx@linutronix.de, pombredanne@nexb.com,
stummala@codeaurora.org, gregkh@linuxfoundation.org,
sfr@canb.auug.org.au, guro@fb.com, mka@chromium.org,
penguin-kernel@I-love.SAKURA.ne.jp, chris@chris-wilson.co.uk,
longman@redhat.com, minchan@kernel.org, ying.huang@intel.com,
mgorman@techsingularity.net, jbacik@fb.com, linux@roeck-us.net,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
willy@infradead.org, lirongqing@baidu.com,
aryabinin@virtuozzo.com
Subject: Re: [PATCH v6 05/17] mm: Assign memcg-aware shrinkers bitmap to memcg
Date: Mon, 21 May 2018 21:40:41 +0300 [thread overview]
Message-ID: <20180521184041.5p2zyhzu45eeihmi@esperanza> (raw)
In-Reply-To: <7a5c644d-625e-a01e-a9a7-304eea13d225@virtuozzo.com>
On Mon, May 21, 2018 at 01:16:40PM +0300, Kirill Tkhai wrote:
> >> +static int memcg_expand_one_shrinker_map(struct mem_cgroup *memcg,
> >> + int size, int old_size)
> >
> > Nit: No point in passing old_size here. You can instead use
> > memcg_shrinker_map_size directly.
>
> This is made for the readability. All the actions with global variable
> is made in the same function -- memcg_expand_shrinker_maps(), all
> the actions with local variables are also in the same -- memcg_expand_one_shrinker_map().
> Accessing memcg_shrinker_map_size in memcg_expand_one_shrinker_map()
> looks not intuitive and breaks modularity.
I guess it depends on how you look at it. Anyway, it's nitpicking so I
won't mind if you leave it as is.
> >> +static int memcg_alloc_shrinker_maps(struct mem_cgroup *memcg)
> >> +{
> >> + struct memcg_shrinker_map *map;
> >> + int nid, size, ret = 0;
> >> +
> >> + if (mem_cgroup_is_root(memcg))
> >> + return 0;
> >> +
> >> + mutex_lock(&memcg_shrinker_map_mutex);
> >> + size = memcg_shrinker_map_size;
> >> + for_each_node(nid) {
> >> + map = kvzalloc(sizeof(*map) + size, GFP_KERNEL);
> >> + if (!map) {
> >
> >> + memcg_free_shrinker_maps(memcg);
> >
> > Nit: Please don't call this function under the mutex as it isn't
> > necessary. Set 'ret', break the loop, then check 'ret' after releasing
> > the mutex, and call memcg_free_shrinker_maps() if it's not 0.
>
> No, it must be called under the mutex. See the race with memcg_expand_one_shrinker_map().
> NULL maps are not expanded, and this is the indicator we use to differ memcg, which is
> not completely online. If the allocations in memcg_alloc_shrinker_maps() fail at nid == 1,
> then freeing of nid == 0 can race with expanding.
Ah, I see, you're right.
> >> diff --git a/mm/vmscan.c b/mm/vmscan.c
> >> index 3de12a9bdf85..f09ea20d7270 100644
> >> --- a/mm/vmscan.c
> >> +++ b/mm/vmscan.c
> >> @@ -171,6 +171,7 @@ static DECLARE_RWSEM(shrinker_rwsem);
> >>
> >> #ifdef CONFIG_MEMCG_KMEM
> >> static DEFINE_IDR(shrinker_idr);
> >
> >> +static int memcg_shrinker_nr_max;
> >
> > Nit: Please rename it to shrinker_id_max and make it store max shrinker
> > id, not the max number shrinkers that have ever been allocated. This
> > will make it easier to understand IMO.
> >
> > Also, this variable doesn't belong to this patch as you don't really
> > need it to expaned mem cgroup maps. Let's please move it to patch 3
> > (the one that introduces shrinker_idr).
> >
> >>
> >> static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> >> {
> >> @@ -181,6 +182,15 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> >> ret = id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
> >> if (ret < 0)
> >> goto unlock;
> >
> >> +
> >> + if (id >= memcg_shrinker_nr_max) {
> >> + if (memcg_expand_shrinker_maps(id + 1)) {
> >> + idr_remove(&shrinker_idr, id);
> >> + goto unlock;
> >> + }
> >> + memcg_shrinker_nr_max = id + 1;
> >> + }
> >> +
> >
> > Then we'll have here:
> >
> > if (memcg_expaned_shrinker_maps(id)) {
> > idr_remove(shrinker_idr, id);
> > goto unlock;
> > }
> >
> > and from patch 3:
> >
> > shrinker_id_max = MAX(shrinker_id_max, id);
>
> So, shrinker_id_max contains "the max number shrinkers that have ever been allocated" minus 1.
> The only difference to existing logic is "minus 1", which will be needed to reflect in
> shrink_slab_memcg()->for_each_set_bit()...
>
> To have "minus 1" instead of "not to have minus 1" looks a little subjective.
OK, leave 'nr' then, but please consider my other comments:
- rename memcg_shrinker_nr_max to shrinker_nr_max so that the variable
name is consistent with shrinker_idr
- move shrinker_nr_max to patch 3 as you don't need it for expanding
memcg shrinker maps
- don't use shrinker_nr_max to check whether we need to expand memcg
maps - simply call memcg_expand_shrinker_maps() and let it decide -
this will neatly isolate all the logic related to memcg shrinker map
allocation in memcontrol.c
next prev parent reply other threads:[~2018-05-21 18:40 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-18 8:41 [PATCH v6 00/17] Improve shrink_slab() scalability (old complexity was O(n^2), new is O(n)) Kirill Tkhai
2018-05-18 8:41 ` [PATCH v6 01/17] list_lru: Combine code under the same define Kirill Tkhai
2018-05-18 8:41 ` [PATCH v6 02/17] mm: Introduce CONFIG_MEMCG_KMEM as combination of CONFIG_MEMCG && !CONFIG_SLOB Kirill Tkhai
2018-05-18 8:42 ` [PATCH v6 03/17] mm: Assign id to every memcg-aware shrinker Kirill Tkhai
2018-05-20 7:08 ` Vladimir Davydov
2018-05-18 8:42 ` [PATCH v6 04/17] memcg: Move up for_each_mem_cgroup{, _tree} defines Kirill Tkhai
2018-05-18 8:42 ` [PATCH v6 05/17] mm: Assign memcg-aware shrinkers bitmap to memcg Kirill Tkhai
2018-05-20 7:27 ` Vladimir Davydov
2018-05-21 10:16 ` Kirill Tkhai
2018-05-21 18:40 ` Vladimir Davydov [this message]
2018-05-18 8:42 ` [PATCH v6 06/17] mm: Refactoring in workingset_init() Kirill Tkhai
2018-05-18 8:42 ` [PATCH v6 07/17] fs: Refactoring in alloc_super() Kirill Tkhai
2018-05-18 8:43 ` [PATCH v6 08/17] fs: Propagate shrinker::id to list_lru Kirill Tkhai
2018-05-18 8:43 ` [PATCH v6 09/17] list_lru: Add memcg argument to list_lru_from_kmem() Kirill Tkhai
2018-05-18 8:43 ` [PATCH v6 10/17] list_lru: Pass dst_memcg argument to memcg_drain_list_lru_node() Kirill Tkhai
2018-05-18 8:43 ` [PATCH v6 11/17] list_lru: Pass lru " Kirill Tkhai
2018-05-18 8:43 ` [PATCH v6 12/17] mm: Set bit in memcg shrinker bitmap on first list_lru item apearance Kirill Tkhai
2018-05-20 7:55 ` Vladimir Davydov
2018-05-21 9:31 ` Kirill Tkhai
2018-05-21 18:16 ` Vladimir Davydov
2018-05-18 8:43 ` [PATCH v6 13/17] mm: Export mem_cgroup_is_root() Kirill Tkhai
2018-05-20 7:57 ` Vladimir Davydov
2018-05-18 8:44 ` [PATCH v6 14/17] mm: Iterate only over charged shrinkers during memcg shrink_slab() Kirill Tkhai
2018-05-20 8:00 ` Vladimir Davydov
2018-05-21 9:17 ` Kirill Tkhai
2018-05-21 17:56 ` Vladimir Davydov
2018-05-18 8:44 ` [PATCH v6 15/17] mm: Generalize shrink_slab() calls in shrink_node() Kirill Tkhai
2018-05-20 8:08 ` Vladimir Davydov
2018-05-21 9:19 ` Kirill Tkhai
2018-05-18 8:44 ` [PATCH v6 16/17] mm: Add SHRINK_EMPTY shrinker methods return value Kirill Tkhai
2018-05-18 8:44 ` [PATCH v6 17/17] mm: Clear shrinker bit if there are no objects related to memcg Kirill Tkhai
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