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Date: Fri, 5 Feb 2021 17:41:34 +0300
From: Kirill Tkhai <ktkhai@...tuozzo.com>
To: Yang Shi <shy828301@...il.com>
Cc: Roman Gushchin <guro@...com>, Vlastimil Babka <vbabka@...e.cz>,
Shakeel Butt <shakeelb@...gle.com>,
Dave Chinner <david@...morbit.com>,
Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...e.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux MM <linux-mm@...ck.org>,
Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [v6 PATCH 08/11] mm: vmscan: use per memcg nr_deferred of
shrinker
On 04.02.2021 20:23, Yang Shi wrote:
> On Thu, Feb 4, 2021 at 12:42 AM Kirill Tkhai <ktkhai@...tuozzo.com> wrote:
>>
>> On 03.02.2021 20:20, Yang Shi wrote:
>>> Use per memcg's nr_deferred for memcg aware shrinkers. The shrinker's nr_deferred
>>> will be used in the following cases:
>>> 1. Non memcg aware shrinkers
>>> 2. !CONFIG_MEMCG
>>> 3. memcg is disabled by boot parameter
>>>
>>> Signed-off-by: Yang Shi <shy828301@...il.com>
>>> ---
>>> mm/vmscan.c | 94 +++++++++++++++++++++++++++++++++++++++++++----------
>>> 1 file changed, 77 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>> index d9126f12890f..545422d2aeec 100644
>>> --- a/mm/vmscan.c
>>> +++ b/mm/vmscan.c
>>> @@ -190,6 +190,13 @@ static int shrinker_nr_max;
>>> #define NR_MAX_TO_SHR_MAP_SIZE(nr_max) \
>>> (DIV_ROUND_UP(nr_max, BITS_PER_LONG) * sizeof(unsigned long))
>>>
>>> +static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
>>> + int nid)
>>> +{
>>> + return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
>>> + lockdep_is_held(&shrinker_rwsem));
>>> +}
>>
>> Thanks for the helper. Why not to introduce and become to use it in old places
>> in a separate patch?
>
> What do you mean about "old places"? Where was it introduced in v5 (in
> patch #10)?
I mean existing places touched by this patch, which became to use the new helper
in this patch: free_shrinker_info(), expand_one_shrinker_info(), shrink_slab_memcg().
>>
>>> +
>>> static void free_shrinker_info_rcu(struct rcu_head *head)
>>> {
>>> kvfree(container_of(head, struct shrinker_info, rcu));
>>> @@ -204,8 +211,7 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
>>> int size = m_size + d_size;
>>>
>>> for_each_node(nid) {
>>> - old = rcu_dereference_protected(
>>> - mem_cgroup_nodeinfo(memcg, nid)->shrinker_info, true);
>>> + old = shrinker_info_protected(memcg, nid);
>>> /* Not yet online memcg */
>>> if (!old)
>>> return 0;
>>> @@ -239,7 +245,7 @@ void free_shrinker_info(struct mem_cgroup *memcg)
>>>
>>> for_each_node(nid) {
>>> pn = mem_cgroup_nodeinfo(memcg, nid);
>>> - info = rcu_dereference_protected(pn->shrinker_info, true);
>>> + info = shrinker_info_protected(memcg, nid);
>>> kvfree(info);
>>> rcu_assign_pointer(pn->shrinker_info, NULL);
>>> }
>>> @@ -358,6 +364,25 @@ static void unregister_memcg_shrinker(struct shrinker *shrinker)
>>> up_write(&shrinker_rwsem);
>>> }
>>>
>>> +
>>> +static long count_nr_deferred_memcg(int nid, struct shrinker *shrinker,
>>> + struct mem_cgroup *memcg)
>>> +{
>>> + struct shrinker_info *info;
>>> +
>>> + info = shrinker_info_protected(memcg, nid);
>>> + return atomic_long_xchg(&info->nr_deferred[shrinker->id], 0);
>>> +}
>>> +
>>> +static long set_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
>>> + struct mem_cgroup *memcg)
>>> +{
>>> + struct shrinker_info *info;
>>> +
>>> + info = shrinker_info_protected(memcg, nid);
>>> + return atomic_long_add_return(nr, &info->nr_deferred[shrinker->id]);
>>> +}
>>
>> Names confuse me a little bit. What about xchg_nr_deferred_memcg() and add_nr_deferred_memcg()?
>
> add_nr_deferred_memcg() sounds more self-explained to me.
>
>>
>>> static bool cgroup_reclaim(struct scan_control *sc)
>>> {
>>> return sc->target_mem_cgroup;
>>> @@ -396,6 +421,18 @@ static void unregister_memcg_shrinker(struct shrinker *shrinker)
>>> {
>>> }
>>>
>>> +static long count_nr_deferred_memcg(int nid, struct shrinker *shrinker,
>>> + struct mem_cgroup *memcg)
>>> +{
>>> + return 0;
>>> +}
>>> +
>>> +static long set_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
>>> + struct mem_cgroup *memcg)
>>> +{
>>> + return 0;
>>> +}
>>> +
>>> static bool cgroup_reclaim(struct scan_control *sc)
>>> {
>>> return false;
>>> @@ -407,6 +444,39 @@ static bool writeback_throttling_sane(struct scan_control *sc)
>>> }
>>> #endif
>>>
>>> +static long count_nr_deferred(struct shrinker *shrinker,
>>> + struct shrink_control *sc)
>>> +{
>>> + int nid = sc->nid;
>>> +
>>> + if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
>>> + nid = 0;
>>> +
>>> + if (sc->memcg &&
>>> + (shrinker->flags & SHRINKER_MEMCG_AWARE))
>>> + return count_nr_deferred_memcg(nid, shrinker,
>>> + sc->memcg);
>>> +
>>> + return atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
>>> +}
>>> +
>>> +
>>> +static long set_nr_deferred(long nr, struct shrinker *shrinker,
>>> + struct shrink_control *sc)
>>> +{
>>> + int nid = sc->nid;
>>> +
>>> + if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
>>> + nid = 0;
>>> +
>>> + if (sc->memcg &&
>>> + (shrinker->flags & SHRINKER_MEMCG_AWARE))
>>> + return set_nr_deferred_memcg(nr, nid, shrinker,
>>> + sc->memcg);
>>> +
>>> + return atomic_long_add_return(nr, &shrinker->nr_deferred[nid]);
>>> +}
>>> +
>>> /*
>>> * This misses isolated pages which are not accounted for to save counters.
>>> * As the data only determines if reclaim or compaction continues, it is
>>> @@ -539,14 +609,10 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
>>> long freeable;
>>> long nr;
>>> long new_nr;
>>> - int nid = shrinkctl->nid;
>>> long batch_size = shrinker->batch ? shrinker->batch
>>> : SHRINK_BATCH;
>>> long scanned = 0, next_deferred;
>>>
>>> - if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
>>> - nid = 0;
>>> -
>>> freeable = shrinker->count_objects(shrinker, shrinkctl);
>>> if (freeable == 0 || freeable == SHRINK_EMPTY)
>>> return freeable;
>>> @@ -556,7 +622,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
>>> * and zero it so that other concurrent shrinker invocations
>>> * don't also do this scanning work.
>>> */
>>> - nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
>>> + nr = count_nr_deferred(shrinker, shrinkctl);
>>>
>>> total_scan = nr;
>>> if (shrinker->seeks) {
>>> @@ -647,14 +713,9 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
>>> next_deferred = 0;
>>> /*
>>> * move the unused scan count back into the shrinker in a
>>> - * manner that handles concurrent updates. If we exhausted the
>>> - * scan, there is no need to do an update.
>>> + * manner that handles concurrent updates.
>>> */
>>> - if (next_deferred > 0)
>>> - new_nr = atomic_long_add_return(next_deferred,
>>> - &shrinker->nr_deferred[nid]);
>>> - else
>>> - new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
>>> + new_nr = set_nr_deferred(next_deferred, shrinker, shrinkctl);
>>>
>>> trace_mm_shrink_slab_end(shrinker, shrinkctl->nid, freed, nr, new_nr, total_scan);
>>> return freed;
>>> @@ -674,8 +735,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
>>> if (!down_read_trylock(&shrinker_rwsem))
>>> return 0;
>>>
>>> - info = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
>>> - true);
>>> + info = shrinker_info_protected(memcg, nid);
>>> if (unlikely(!info))
>>> goto unlock;
>>>
>>>
>>
>>
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