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[124.209.188.1]) by smtp.gmail.com with ESMTPSA id l17-20020a170903245100b001b1920cffd5sm3246036pls.267.2023.06.17.22.30.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 17 Jun 2023 22:30:53 -0700 (PDT) Date: Sun, 18 Jun 2023 14:30:48 +0900 From: Sergey Senozhatsky To: Yosry Ahmed Cc: Sergey Senozhatsky , Domenico Cerasuolo , vitaly.wool@konsulko.com, minchan@kernel.org, linux-mm@kvack.org, ddstreet@ieee.org, sjenning@redhat.com, nphamcs@gmail.com, hannes@cmpxchg.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v3 1/7] mm: zswap: add pool shrinking mechanism Message-ID: <20230618053048.GC2417524@google.com> References: <20230612093815.133504-1-cerasuolodomenico@gmail.com> <20230612093815.133504-2-cerasuolodomenico@gmail.com> <20230618043857.GA2417524@google.com> <20230618052526.GB2417524@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: C028FC0016 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: jq11bugaz17we8a7ix9krkjs7srzua8y X-HE-Tag: 1687066254-526107 X-HE-Meta: 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 u2F72TJH Ww2jjoYC/CKnE1r1yw8F23ofzWxtQwdXlFieaNgFMEDUiGqIQ+0UOLOGAjN6EcJiKdrYo5+YVNRAre4tCsR9mp9O8SLVTwrSSbvHg3WlrZy41k5B7QvY7c3VYQsyQ5ILzLXDtw9kFsc9VbXq0FL8WDHCYrtpdf2kaCTQs871yIn9ncDRxp0UKx/PH/4t1ihhzw1gwWbnxerKP50iOrrvw+v/KoJDPw4eso/8mVvqjjZBp56JmhAOZbbUVvKa7SgMz3DAQGWOQzx3/c13rKSaRQVo7CnxHUnBpDQ1jLflmnsnmp8Gep+3X+kdOQgiX0WDQcr67DHhfQ6oLyEnd7teWGaezpLFPd7T7wVSS 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 (23/06/17 22:28), Yosry Ahmed wrote: > > On (23/06/17 21:48), Yosry Ahmed wrote: > > > > On (23/06/12 11:38), Domenico Cerasuolo wrote: > > > > > +static int zswap_reclaim_entry(struct zswap_pool *pool) > > > > > +{ > > > > > + struct zswap_header *zhdr; > > > > > + struct zswap_entry *entry; > > > > > + struct zswap_tree *tree; > > > > > + pgoff_t swpoffset; > > > > > + int ret; > > > > > + > > > > > + /* Get an entry off the LRU */ > > > > > + spin_lock(&pool->lru_lock); > > > > > + if (list_empty(&pool->lru)) { > > > > > + spin_unlock(&pool->lru_lock); > > > > > + return -EINVAL; > > > > > + } > > > > > + entry = list_last_entry(&pool->lru, struct zswap_entry, lru); > > > > > + list_del_init(&entry->lru); > > > > > > > > A quick question: should we zswap_entry_get() here? > > > > > > We need to hold the tree lock for that, and the lock ordering is tree > > > lock -> lru lock. If we try to grab the tree lock here we may > > > deadlock. > > > > We can deadlock doing this? > > > > lock tree_lock > > lock lru_lock > > list_del_init > > unlock lru_lock > > entry_get > > unlock tree_lock > > writeback > > We don't know which tree the zswap entry belongs to Oh... I must be blind. You are right. Sorry for the noise.