From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DEFAF33B96D for ; Fri, 21 Nov 2025 08:18:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763713095; cv=none; b=Y40+aWmi6cf+tShtdAtnw5442Q+OKmhqIAuSxho73U+cmkGJtFehT/uNQGtlm97mnIcGvRJPxg4ikBhreg5AzIgq6X+ng8AhmAuIy7A3nsFbd+yyFUrTnO5TM84lk/8XOpvQBXzUzIVhSuGJvvX0dOFKfivHxyyAIjhRtuIPqRw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763713095; c=relaxed/simple; bh=WnTPt8wuqcGBFvPOaOIvOJFtAEJbuOKn1WNGNugp2UM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=TclQ7camzwdojDPyvBJZ1FpRU2dcH91Rnkb9Xx7yseIXTu2e4U5RB4voeugBTU1w/WtqzlR+VDGzTMk5/PpJT76OCvXLloy8hVla9OgoHIvEacPNvJk+vlVSEUDAD/602sz/7gtqI81eNBpOZRXi6Weii4GaIjncLrwAnJIx1pA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=l9cINglt; arc=none smtp.client-ip=91.218.175.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="l9cINglt" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1763713087; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6j/lGFm/xWvuyqpIw5QwOUGYGHYdfUywDo5MBgkolKk=; b=l9cINgltohrtcBrc+2AtYmFNx8lZUo78oRgRikFYsusMSs99QnTpPxcYIQXUPu1wyugYP8 iJkure1G943I4FPT/NCqiPEGjQaOP5goQgwlF5oWncxnldZqeUfOCLb1/dg3cED7tv6hL8 kQQWjvNpP0As3m+DftnL7if3nTiV5hc= Date: Fri, 21 Nov 2025 16:17:52 +0800 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v1 05/26] mm: memcontrol: allocate object cgroup for non-kmem case To: Chen Ridong , hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, david@redhat.com, lorenzo.stoakes@oracle.com, ziy@nvidia.com, harry.yoo@oracle.com, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Muchun Song , Qi Zheng References: <05ef300193bbe5bb7d2d97723efe928dab60429b.1761658310.git.zhengqi.arch@bytedance.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 11/21/25 11:58 AM, Chen Ridong wrote: > > > On 2025/10/28 21:58, Qi Zheng wrote: >> From: Muchun Song >> >> Pagecache pages are charged at allocation time and hold a reference >> to the original memory cgroup until reclaimed. Depending on memory >> pressure, page sharing patterns between different cgroups and cgroup >> creation/destruction rates, many dying memory cgroups can be pinned >> by pagecache pages, reducing page reclaim efficiency and wasting >> memory. Converting LRU folios and most other raw memory cgroup pins >> to the object cgroup direction can fix this long-living problem. >> >> As a result, the objcg infrastructure is no longer solely applicable >> to the kmem case. In this patch, we extend the scope of the objcg >> infrastructure beyond the kmem case, enabling LRU folios to reuse >> it for folio charging purposes. >> >> It should be noted that LRU folios are not accounted for at the root >> level, yet the folio->memcg_data points to the root_mem_cgroup. Hence, >> the folio->memcg_data of LRU folios always points to a valid pointer. >> However, the root_mem_cgroup does not possess an object cgroup. >> Therefore, we also allocate an object cgroup for the root_mem_cgroup. >> >> Signed-off-by: Muchun Song >> Signed-off-by: Qi Zheng >> --- >> mm/memcontrol.c | 51 +++++++++++++++++++++++-------------------------- >> 1 file changed, 24 insertions(+), 27 deletions(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index d5257465c9d75..2afd7f99ca101 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -204,10 +204,10 @@ static struct obj_cgroup *obj_cgroup_alloc(void) >> return objcg; >> } >> >> -static void memcg_reparent_objcgs(struct mem_cgroup *memcg, >> - struct mem_cgroup *parent) >> +static void memcg_reparent_objcgs(struct mem_cgroup *memcg) >> { >> struct obj_cgroup *objcg, *iter; >> + struct mem_cgroup *parent = parent_mem_cgroup(memcg); >> >> objcg = rcu_replace_pointer(memcg->objcg, NULL, true); >> >> @@ -3302,30 +3302,17 @@ unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap) >> return val; >> } >> >> -static int memcg_online_kmem(struct mem_cgroup *memcg) >> +static void memcg_online_kmem(struct mem_cgroup *memcg) >> { >> - struct obj_cgroup *objcg; >> - >> if (mem_cgroup_kmem_disabled()) >> - return 0; >> + return; >> >> if (unlikely(mem_cgroup_is_root(memcg))) >> - return 0; >> - >> - objcg = obj_cgroup_alloc(); >> - if (!objcg) >> - return -ENOMEM; >> - >> - objcg->memcg = memcg; >> - rcu_assign_pointer(memcg->objcg, objcg); >> - obj_cgroup_get(objcg); >> - memcg->orig_objcg = objcg; >> + return; >> >> static_branch_enable(&memcg_kmem_online_key); >> >> memcg->kmemcg_id = memcg->id.id; >> - >> - return 0; >> } >> >> static void memcg_offline_kmem(struct mem_cgroup *memcg) >> @@ -3340,12 +3327,6 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg) >> >> parent = parent_mem_cgroup(memcg); >> memcg_reparent_list_lrus(memcg, parent); >> - >> - /* >> - * Objcg's reparenting must be after list_lru's, make sure list_lru >> - * helpers won't use parent's list_lru until child is drained. >> - */ >> - memcg_reparent_objcgs(memcg, parent); >> } >> >> #ifdef CONFIG_CGROUP_WRITEBACK >> @@ -3862,9 +3843,9 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css) >> static int mem_cgroup_css_online(struct cgroup_subsys_state *css) >> { >> struct mem_cgroup *memcg = mem_cgroup_from_css(css); >> + struct obj_cgroup *objcg; >> >> - if (memcg_online_kmem(memcg)) >> - goto remove_id; >> + memcg_online_kmem(memcg); >> >> /* >> * A memcg must be visible for expand_shrinker_info() >> @@ -3874,6 +3855,15 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css) >> if (alloc_shrinker_info(memcg)) >> goto offline_kmem; >> >> + objcg = obj_cgroup_alloc(); >> + if (!objcg) >> + goto free_shrinker; >> + >> + objcg->memcg = memcg; >> + rcu_assign_pointer(memcg->objcg, objcg); >> + obj_cgroup_get(objcg); >> + memcg->orig_objcg = objcg; >> + > > Will it be better to add a helper function like obj_cgroup_init()? This part is not complicated, and it is only called in this one place, so perhaps there is no need to add a helper function? Of course, it doesn't matter, I'm fine with either method. > >> if (unlikely(mem_cgroup_is_root(memcg)) && !mem_cgroup_disabled()) >> queue_delayed_work(system_unbound_wq, &stats_flush_dwork, >> FLUSH_TIME); >> @@ -3896,9 +3886,10 @@ static int mem_cgroup_css_online(struct cgroup_subsys_state *css) >> xa_store(&mem_cgroup_ids, memcg->id.id, memcg, GFP_KERNEL); >> >> return 0; >> +free_shrinker: >> + free_shrinker_info(memcg); >> offline_kmem: >> memcg_offline_kmem(memcg); >> -remove_id: >> mem_cgroup_id_remove(memcg); >> return -ENOMEM; >> } >> @@ -3916,6 +3907,12 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css) >> >> memcg_offline_kmem(memcg); >> reparent_deferred_split_queue(memcg); >> + /* >> + * The reparenting of objcg must be after the reparenting of the >> + * list_lru and deferred_split_queue above, which ensures that they will >> + * not mistakenly get the parent list_lru and deferred_split_queue. >> + */ >> + memcg_reparent_objcgs(memcg); >> reparent_shrinker_deferred(memcg); >> wb_memcg_offline(memcg); >> lru_gen_offline_memcg(memcg); >