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Sat, 17 Jun 2023 22:32:15 -0700 (PDT) MIME-Version: 1.0 References: <20230612093815.133504-1-cerasuolodomenico@gmail.com> <20230612093815.133504-2-cerasuolodomenico@gmail.com> <20230618043857.GA2417524@google.com> <20230618052526.GB2417524@google.com> <20230618053048.GC2417524@google.com> In-Reply-To: <20230618053048.GC2417524@google.com> From: Yosry Ahmed Date: Sat, 17 Jun 2023 22:31:39 -0700 Message-ID: Subject: Re: [PATCH v3 1/7] mm: zswap: add pool shrinking mechanism To: Sergey Senozhatsky Cc: 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 0C8624000D X-Rspam-User: X-Stat-Signature: 3jhd3pfrsxsttrz5jt3epajxed9wrigm X-Rspamd-Server: rspam01 X-HE-Tag: 1687066336-554779 X-HE-Meta: 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 6nEIFc6w 5j8nMIN5R39wefI1NO3XJt8hs4wwkbqruBp8Q0Sfn9xuVAiWy5afOo3qX4FswCxYyT7zNZ9K3sPhybQVzr95Q24yXVLhZyh5a0t/HWomo2kB9CqieoaEXe4UbL8pd3cffUBH80VZcw3uQYAvLDjIj4u1ZPCsMD6E6sF7mcQlnXeS3k0RSKSDzlLVQ2k9lhGWGmvWhegOr6aoyOoUYaJYUx7WH8PvvWsbur68odw5tIGcoBYac8Bp7EV7q123kx7RUyj0tJ1+21E6snE33qaNVzgIUJslJu6r/QRya 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 Sat, Jun 17, 2023 at 10:30=E2=80=AFPM Sergey Senozhatsky wrote: > > 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 =3D 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 tr= ee > > > > 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. Don't blame yourself, it is fairly convoluted :)