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Message-ID: <12b23c89-c7b1-56b3-5cff-1e1b07e24de6@nextfour.com>
Date: Mon, 20 Dec 2021 11:27:03 +0200
From: Mika Penttilä <mika.penttila@...tfour.com>
To: Muchun Song <songmuchun@...edance.com>, willy@...radead.org,
akpm@...ux-foundation.org, hannes@...xchg.org, mhocko@...nel.org,
vdavydov.dev@...il.com, shakeelb@...gle.com, guro@...com,
shy828301@...il.com, alexs@...nel.org, richard.weiyang@...il.com,
david@...morbit.com, trond.myklebust@...merspace.com,
anna.schumaker@...app.com, jaegeuk@...nel.org, chao@...nel.org,
kari.argillander@...il.com
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, linux-nfs@...r.kernel.org,
zhengqi.arch@...edance.com, duanxiongchun@...edance.com,
fam.zheng@...edance.com, smuchun@...il.com
Subject: Re: [PATCH v5 13/16] mm: memcontrol: reuse memory cgroup ID for kmem
ID
Hi,
On 20.12.2021 10.56, Muchun Song wrote:
> There are two idrs being used by memory cgroup, one is for kmem ID,
> another is for memory cgroup ID. The maximum ID of both is 64Ki.
> Both of them can limit the total number of memory cgroups. Actually,
> we can reuse memory cgroup ID for kmem ID to simplify the code.
>
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
> include/linux/memcontrol.h | 1 +
> mm/memcontrol.c | 46 ++++++++--------------------------------------
> 2 files changed, 9 insertions(+), 38 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 3fc437162add..7b472f805d77 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -56,6 +56,7 @@ struct mem_cgroup_reclaim_cookie {
> #ifdef CONFIG_MEMCG
>
> #define MEM_CGROUP_ID_SHIFT 16
> +#define MEM_CGROUP_ID_MIN 1
> #define MEM_CGROUP_ID_MAX USHRT_MAX
>
> struct mem_cgroup_id {
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 28d6d2564f9d..04f75055f518 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -348,23 +348,6 @@ static void memcg_reparent_objcgs(struct mem_cgroup *memcg,
> }
>
> /*
> - * This will be used as a shrinker list's index.
> - * The main reason for not using cgroup id for this:
> - * this works better in sparse environments, where we have a lot of memcgs,
> - * but only a few kmem-limited.
> - */
> -static DEFINE_IDA(memcg_cache_ida);
> -
> -/*
> - * MAX_SIZE should be as large as the number of cgrp_ids. Ideally, we could get
> - * this constant directly from cgroup, but it is understandable that this is
> - * better kept as an internal representation in cgroup.c. In any case, the
> - * cgrp_id space is not getting any smaller, and we don't have to necessarily
> - * increase ours as well if it increases.
> - */
> -#define MEMCG_CACHES_MAX_SIZE MEM_CGROUP_ID_MAX
> -
> -/*
> * A lot of the calls to the cache allocation functions are expected to be
> * inlined by the compiler. Since the calls to memcg_slab_pre_alloc_hook() are
> * conditional to this static branch, we'll have to allow modules that does
> @@ -3528,10 +3511,12 @@ static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css,
> }
>
> #ifdef CONFIG_MEMCG_KMEM
> +#define MEM_CGROUP_KMEM_ID_MIN -1
Maybe
#define MEM_CGROUP_KMEM_ID_MIN 0
to be the first allocated id, so MEM_CGROUP_ID_DIFF is 1, not 2
> +#define MEM_CGROUP_ID_DIFF (MEM_CGROUP_ID_MIN - MEM_CGROUP_KMEM_ID_MIN)
> +
> static int memcg_online_kmem(struct mem_cgroup *memcg)
> {
> struct obj_cgroup *objcg;
> - int memcg_id;
>
> if (cgroup_memory_nokmem)
> return 0;
> @@ -3539,22 +3524,16 @@ static int memcg_online_kmem(struct mem_cgroup *memcg)
> if (unlikely(mem_cgroup_is_root(memcg)))
> return 0;
>
> - memcg_id = ida_alloc_max(&memcg_cache_ida, MEMCG_CACHES_MAX_SIZE - 1,
> - GFP_KERNEL);
> - if (memcg_id < 0)
> - return memcg_id;
> -
> objcg = obj_cgroup_alloc();
> - if (!objcg) {
> - ida_free(&memcg_cache_ida, memcg_id);
> + if (!objcg)
> return -ENOMEM;
> - }
> +
> objcg->memcg = memcg;
> rcu_assign_pointer(memcg->objcg, objcg);
>
> static_branch_enable(&memcg_kmem_enabled_key);
>
> - memcg->kmemcg_id = memcg_id;
> + memcg->kmemcg_id = memcg->id.id - MEM_CGROUP_ID_DIFF;
>
> return 0;
> }
> @@ -3562,7 +3541,6 @@ static int memcg_online_kmem(struct mem_cgroup *memcg)
> static void memcg_offline_kmem(struct mem_cgroup *memcg)
> {
> struct mem_cgroup *parent;
> - int kmemcg_id;
>
> if (cgroup_memory_nokmem)
> return;
> @@ -3577,20 +3555,12 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
> memcg_reparent_objcgs(memcg, parent);
>
> /*
> - * memcg_reparent_list_lrus() can change memcg->kmemcg_id.
> - * Cache it to local @kmemcg_id.
> - */
> - kmemcg_id = memcg->kmemcg_id;
> -
> - /*
> * After we have finished memcg_reparent_objcgs(), all list_lrus
> * corresponding to this cgroup are guaranteed to remain empty.
> * The ordering is imposed by list_lru_node->lock taken by
> * memcg_reparent_list_lrus().
> */
> memcg_reparent_list_lrus(memcg, parent);
> -
> - ida_free(&memcg_cache_ida, kmemcg_id);
> }
> #else
> static int memcg_online_kmem(struct mem_cgroup *memcg)
> @@ -5043,7 +5013,7 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
> return ERR_PTR(error);
>
> memcg->id.id = idr_alloc(&mem_cgroup_idr, NULL,
> - 1, MEM_CGROUP_ID_MAX,
> + MEM_CGROUP_ID_MIN, MEM_CGROUP_ID_MAX,
> GFP_KERNEL);
> if (memcg->id.id < 0) {
> error = memcg->id.id;
> @@ -5071,7 +5041,7 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
> spin_lock_init(&memcg->event_list_lock);
> memcg->socket_pressure = jiffies;
> #ifdef CONFIG_MEMCG_KMEM
> - memcg->kmemcg_id = -1;
> + memcg->kmemcg_id = MEM_CGROUP_KMEM_ID_MIN;
> INIT_LIST_HEAD(&memcg->objcg_list);
> #endif
> #ifdef CONFIG_CGROUP_WRITEBACK
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