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Date: Thu, 6 Jan 2022 11:34:58 +0800 From: Muchun Song <songmuchun@...edance.com> To: Michal Koutný <mkoutny@...e.com>, Mika Penttilä <mika.penttila@...tfour.com> Cc: Matthew Wilcox <willy@...radead.org>, Andrew Morton <akpm@...ux-foundation.org>, Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, Vladimir Davydov <vdavydov.dev@...il.com>, Shakeel Butt <shakeelb@...gle.com>, Roman Gushchin <guro@...com>, Yang Shi <shy828301@...il.com>, Alex Shi <alexs@...nel.org>, Wei Yang <richard.weiyang@...il.com>, Dave Chinner <david@...morbit.com>, trond.myklebust@...merspace.com, anna.schumaker@...app.com, jaegeuk@...nel.org, chao@...nel.org, Kari Argillander <kari.argillander@...il.com>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Linux Memory Management List <linux-mm@...ck.org>, linux-nfs@...r.kernel.org, Qi Zheng <zhengqi.arch@...edance.com>, Xiongchun duan <duanxiongchun@...edance.com>, Fam Zheng <fam.zheng@...edance.com>, Muchun Song <smuchun@...il.com> Subject: Re: [PATCH v5 13/16] mm: memcontrol: reuse memory cgroup ID for kmem ID On Thu, Jan 6, 2022 at 1:03 AM Michal Koutný <mkoutny@...e.com> wrote: > > On Mon, Dec 20, 2021 at 04:56:46PM +0800, Muchun Song <songmuchun@...edance.com> 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. > > An interesting improvement. > > I'm a bit dense -- what's the purpose the MEM_CGROUP_ID_DIFF offset? Hi Michal and Mika, MEM_CGROUP_ID_DIFF is introduced to be consistent with before that kmem ID starts with -1 and has no holes. Actually, it can be dropped and make memcg->kmemcg_id equal to memcg->id.id directly. > Couldn't this deduplication be extended to only use mem_cgroup.id.id > instead of mem_cgroup.kmemcg_id? (With a boolean telling whether kmem > accounting is active.) > Not easy to completely remove memcg->kmemcg_id since this filed will be used to sync list_lru reparenting which will change memcg->kmemcg_id to its parent's kmem ID (more details refers to memcg_drain_all_list_lrus() in patch 10 of this series). Thanks.
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