Re: [v6 PATCH 09/11] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers
From: Kirill Tkhai <hidden>
Date: 2021-02-04 09:31:17
Also in:
linux-fsdevel, lkml
On 03.02.2021 20:20, Yang Shi wrote:
quoted hunk ↗ jump to hunk
Now nr_deferred is available on per memcg level for memcg aware shrinkers, so don't need allocate shrinker->nr_deferred for such shrinkers anymore. The prealloc_memcg_shrinker() would return -ENOSYS if !CONFIG_MEMCG or memcg is disabled by kernel command line, then shrinker's SHRINKER_MEMCG_AWARE flag would be cleared. This makes the implementation of this patch simpler. Acked-by: Vlastimil Babka <redacted> Signed-off-by: Yang Shi <redacted> --- mm/vmscan.c | 31 ++++++++++++++++--------------- 1 file changed, 16 insertions(+), 15 deletions(-)diff --git a/mm/vmscan.c b/mm/vmscan.c index 545422d2aeec..20a35d26ae12 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c@@ -334,6 +334,9 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker) { int id, ret = -ENOMEM; + if (mem_cgroup_disabled()) + return -ENOSYS; + down_write(&shrinker_rwsem); /* This may call shrinker, so it must use down_read_trylock() */ id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);@@ -414,7 +417,7 @@ static bool writeback_throttling_sane(struct scan_control *sc) #else static int prealloc_memcg_shrinker(struct shrinker *shrinker) { - return 0; + return -ENOSYS; } static void unregister_memcg_shrinker(struct shrinker *shrinker)@@ -525,8 +528,18 @@ unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone */ int prealloc_shrinker(struct shrinker *shrinker) { - unsigned int size = sizeof(*shrinker->nr_deferred); + unsigned int size; + int err; + + if (shrinker->flags & SHRINKER_MEMCG_AWARE) { + err = prealloc_memcg_shrinker(shrinker); + if (err != -ENOSYS) + return err; + shrinker->flags &= ~SHRINKER_MEMCG_AWARE; + } + + size = sizeof(*shrinker->nr_deferred); if (shrinker->flags & SHRINKER_NUMA_AWARE) size *= nr_node_ids;
This may sound surprisingly, but IIRC do_shrink_slab() may be called on early boot *even before* root_mem_cgroup is allocated. AFAIR, I received syzcaller crash report because of this, when I was implementing shrinker_maps. This is a reason why we don't use shrinker_maps even in case of mem cgroup is not disabled: we iterate every shrinker of shrinker_list. See check in shrink_slab(): if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg)) Possible, we should do the same for nr_deferred: 1)always allocate shrinker->nr_deferred, 2)use shrinker->nr_deferred in count_nr_deferred() and set_nr_deferred().
quoted hunk ↗ jump to hunk
@@ -534,26 +547,14 @@ int prealloc_shrinker(struct shrinker *shrinker) if (!shrinker->nr_deferred) return -ENOMEM; - if (shrinker->flags & SHRINKER_MEMCG_AWARE) { - if (prealloc_memcg_shrinker(shrinker)) - goto free_deferred; - } return 0; - -free_deferred: - kfree(shrinker->nr_deferred); - shrinker->nr_deferred = NULL; - return -ENOMEM; } void free_prealloced_shrinker(struct shrinker *shrinker) { - if (!shrinker->nr_deferred) - return; - if (shrinker->flags & SHRINKER_MEMCG_AWARE) - unregister_memcg_shrinker(shrinker); + return unregister_memcg_shrinker(shrinker); kfree(shrinker->nr_deferred); shrinker->nr_deferred = NULL;