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Wed, 27 Sep 2023 13:51:54 -0700 (PDT) Received: from localhost ([2620:10d:c091:400::5:ba06]) by smtp.gmail.com with ESMTPSA id w19-20020ac86b13000000b00417f330026bsm5001070qts.49.2023.09.27.13.51.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 Sep 2023 13:51:54 -0700 (PDT) Date: Wed, 27 Sep 2023 16:51:53 -0400 From: Johannes Weiner To: Yosry Ahmed Cc: Nhat Pham , akpm@linux-foundation.org, cerasuolodomenico@gmail.com, sjenning@redhat.com, ddstreet@ieee.org, vitaly.wool@konsulko.com, mhocko@kernel.org, roman.gushchin@linux.dev, shakeelb@google.com, muchun.song@linux.dev, linux-mm@kvack.org, kernel-team@meta.com, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Chris Li Subject: Re: [PATCH v2 1/2] zswap: make shrinking memcg-aware Message-ID: <20230927205153.GB399644@cmpxchg.org> References: <20230919171447.2712746-1-nphamcs@gmail.com> <20230919171447.2712746-2-nphamcs@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: A3B3B14000A X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 6rjmxtwkbku3tp7143dur8zzs5i7ny44 X-HE-Tag: 1695847915-978429 X-HE-Meta: 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 /F/etrwS 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 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: On Mon, Sep 25, 2023 at 01:17:04PM -0700, Yosry Ahmed wrote: > On Tue, Sep 19, 2023 at 10:14 AM Nhat Pham wrote: > > + is_empty = false; > > + } > > + zswap_pool_put(pool); > > + > > + if (is_empty) > > + return -EINVAL; > > + if (shrunk) > > + return 0; > > + return -EAGAIN; > > } > > > > static void shrink_worker(struct work_struct *w) > > { > > struct zswap_pool *pool = container_of(w, typeof(*pool), > > shrink_work); > > - int ret, failures = 0; > > + int ret, failures = 0, memcg_selection_failures = 0; > > > > + /* global reclaim will select cgroup in a round-robin fashion. */ > > do { > > - ret = zswap_reclaim_entry(pool); > > + /* previous next_shrink has become a zombie - restart from the top */ > > Do we skip zombies because all zswap entries are reparented with the objcg? > > If yes, why do we restart from the top instead of just skipping them? > memcgs after a zombie will not be reachable now IIUC. > > Also, why explicitly check for zombies instead of having > shrink_memcg() just skip memcgs with no zswap entries? The logic is > slightly complicated. I think this might actually be a leftover from the initial plan to do partial walks without holding on to a reference to the last scanned css. Similar to mem_cgroup_iter() does with the reclaim cookie - if a dead cgroup is encountered and we lose the tree position, restart. But now the code actually holds a reference, so I agree the zombie thing should just be removed.