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([2601:408:c101:1d00:6621:a07c:fed4:cbba]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-47ae9ce292esm48515801cf.63.2025.04.21.17.39.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 21 Apr 2025 17:39:05 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <48a24cb3-16dd-4fb9-9e52-ed82a68041e8@redhat.com> Date: Mon, 21 Apr 2025 20:39:04 -0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/2] vmscan,cgroup: apply mems_effective to reclaim To: Shakeel Butt , Gregory Price Cc: Waiman Long , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, muchun.song@linux.dev, tj@kernel.org, mkoutny@suse.com, akpm@linux-foundation.org References: <20250419053824.1601470-1-gourry@gourry.net> <20250419053824.1601470-3-gourry@gourry.net> <7dtp6v5evpz5sdevwrexhwcdtl5enczssvuepkib2oiaexk3oo@ranij7pskrhe> In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: jlBE9O-4m94uvoqTgTyRwJDNDpjYb9FHsdHcK3jnTdQ_1745282346 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: A6AD840003 X-Rspam-User: X-Stat-Signature: bbm4w7ymi8j6p33g58zznprpg6qmexqk X-HE-Tag: 1745282349-873545 X-HE-Meta: U2FsdGVkX194cvlG4WTWHL49mhO6IBMpf8aqhvdfsTTcmqCwMkIZ9mBDaH3y/K9ytAAUY16zDlM0VxWKSfeMzOs3P43q7unLXSeclkjW/FQNx45l05eqIJHsw+zCs4tJwxY/vGc4Eqa5Je1EWH+pBgC33w9HJr5xZnpoA05EhyfiGoN8cJ6mQaTBh4SJV2NsmHZRR/HGGyVdAgaNgjbQz5YCoxGteTyo+J3K70LSPek8Apmc4fOQNHUMmlsWoGl6hSKAdV/1QFHi+ZRmQUrEcrdtLsqgmKazqCY/vwEKRCb4jtF49muY42gesuo8+y9KxV+PmDkffIe2A9aq3ucxA+Pl5yPCie0i2evBaaW3/CDZqBr38pWUi4J3kbLuD2dW50EGiaBzuvbu84Tuso4E+tHp1kYV7Dw4/Yee1mCtvHV5i+Tt8FBe11NMqeRlk5vuUtvsxWsZN0pPsijmaM9ZZ69j8RIus/vk80nCa0JNCHxrZzLz+6o4dUABnyUGhHJ/eXVvGDRikXDXffKCRHWRQ9zujldrhJXw2JKNu6F6E090Hwema2ufwKS7QtH9u/GGgeV60yw8PqclBXU8pzTWAAsrxeyrkJMGHkkih8kehozH9ftfqy+OgVdKEVbubc6VDAs0deBGYpHswIRgrrRS5lNnGgV2TinEvQcaQ4OpIDdN96jMof3xMclHbxcPAnTnzKSxwKUsuEGIaJJZcrXNEXBlLTQjDSwMG7e+yQcmZeV2MAODpwJmW7yvrwJeptF/BAXG29h7H9G3vZu1r3+70qgHL0w44AQiR3a8mGh3XfUEmVewq/70gUKKgacRlTSV+g9+TVAG0VbCHR40HDk1OTXwi5M3sSXvtrDFAbdTyIPCSoLwhA+20OCv24yyiMKwUOnKXsVhfmWIUXeaytyQQQglTo8TCk913OmU+phaf1t3G0EEAG+0s/u+YU8NRMuaqjKHeGANSBUuDjODO2H R7Zm0LOP Y9yQtaetH/o6UsL+lEbGHO3kct8n8YAdjIJa3GLwDBLn2U6ugkM+HcPc0lEKJRpKGQDBIA6yu5gRkyV9b818iYutF/wke/+WKqx+HAz4KsCzQuQrR+7wyIHOBG3mDHPIhmo2Sa5dtHI2PpHpr778LM8rIhvaE+m+SJrp3+PGgTItzFY7P4FbfaqdpgizHwm4apN0vfeGZ0qENvVBs/l1C6nHfwJYNZBLX3bvyegtsfzpa+B5XuKzETuRyYCrvxK3qxQilJZVCVgy7RgfWG3XXb8LMoxEQ33TbXECkk1e/3UjXmQP8x/rrDht+osADKmCmQ74YnMyEwxZeVzkC8QBDY8o9QC9A7kGCHtViZK6BQssQhMCUpXXNwHAz4fY2iFA+09+22nojUs9AjSDvPZxyZ5CmHofaHDiinoRkbVHoeFlOQbZr8Mh6gDxaquKbMJR83DSy4im1t/yslXzXa+YeG8zdhbb+qjCibvTd X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/21/25 8:10 PM, Shakeel Butt wrote: > On Mon, Apr 21, 2025 at 07:58:44PM -0400, Gregory Price wrote: >> On Mon, Apr 21, 2025 at 04:15:49PM -0700, Shakeel Butt wrote: >>> On Mon, Apr 21, 2025 at 06:59:20PM -0400, Gregory Price wrote: >>>> On Mon, Apr 21, 2025 at 10:39:58AM -0700, Shakeel Butt wrote: >>>>> On Sat, Apr 19, 2025 at 08:14:29PM -0400, Waiman Long wrote: >>>>>> On 4/19/25 2:48 PM, Shakeel Butt wrote: >>>>>>> On Sat, Apr 19, 2025 at 01:38:24AM -0400, Gregory Price wrote: >>>>>>>> +bool cpuset_node_allowed(struct cgroup *cgroup, int nid) >>>>>>>> +{ >>>>>>>> + struct cgroup_subsys_state *css; >>>>>>>> + unsigned long flags; >>>>>>>> + struct cpuset *cs; >>>>>>>> + bool allowed; >>>>>>>> + >>>>>>>> + css = cgroup_get_e_css(cgroup, &cpuset_cgrp_subsys); >>>>>>>> + if (!css) >>>>>>>> + return true; >>>>>>>> + >>>>>>>> + cs = container_of(css, struct cpuset, css); >>>>>>>> + spin_lock_irqsave(&callback_lock, flags); >>>>>>> Do we really need callback_lock here? We are not modifying and I am >>>>>>> wondering if simple rcu read lock is enough here (similar to >>>>>>> update_nodemasks_hier() where parent's effective_mems is accessed within >>>>>>> rcu read lock). >>>>>> The callback_lock is required to ensure the stability of the effective_mems >>>>>> which may be in the process of being changed if not taken. >>>>> Stability in what sense? effective_mems will not get freed under us >>>>> here or is there a chance for corrupted read here? node_isset() and >>>>> nodes_empty() seems atomic. What's the worst that can happen without >>>>> callback_lock? >>>> Fairly sure nodes_empty is not atomic, it's a bitmap search. >>> For bitmaps smaller than 64 bits, it seems atomic and MAX_NUMNODES seems >>> smaller than 64 in all the archs. >> Unfortunately, it's config-defined on (NODES_SHIFT) and the max is 1024. >> >> Is there an argument here for ignoring v1 and just doing the bit-check >> without the lock? Is there an easy ifdef way for us to just return true >> if it's v1? >> > It is !(cgroup_subsys_on_dfl(cpuset_cgrp_subsys)) and I see cpuset_v2() > and is_in_v2_mode() in kernel/cgroup/cpuset.c. The is_in_v2_mode() function covers cpuset2 and cpuset1 with cpuset_v2_mode mount option, while the cpuset_v2() will only be true for cpuset2 and allowing compiling code out in case CPUSETS_V1 isn't set. Cheers, Longman >