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AJvYcCUAufQJvdlluoItJTfjrxBVEmDEScbtjb7KSzVGRkcbb68Zaj2Z4QDdvziqDBbBMBfoWsp4fACAnJgDQF3j60hgW2A= X-Gm-Message-State: AOJu0Yx/lNOOfILpUUlyH7EtgRHN4mMDZ+JqfI8Jg3m9KDTTM20FJNyz NuCGPEK0ubWIAMDeGRMrb1daQIc2jFgmbkxTVAgwMjIiCDQqral8DZxvpidhx+L/KpmXr5whhVb WeGA0tUO6gUssgl/PqIY1Mk1JIEg= X-Google-Smtp-Source: AGHT+IGJQzKrUtwgpXTD2YBmrKy4KAaGfAg2+NxxIhvC+ziLy+gmkCGfvVZN1Osa98tYSGutnyTwYZh+/tJEx0weIaw= X-Received: by 2002:a81:4f87:0:b0:627:df2a:6306 with SMTP id 00721157ae682-62cd55e0bb4mr127824657b3.21.1718129715813; Tue, 11 Jun 2024 11:15:15 -0700 (PDT) MIME-Version: 1.0 References: <20240608155316.451600-1-flintglass@gmail.com> <20240608155316.451600-3-flintglass@gmail.com> In-Reply-To: From: Nhat Pham Date: Tue, 11 Jun 2024 11:15:05 -0700 Message-ID: Subject: Re: [PATCH v1 2/3] mm: zswap: fix global shrinker error handling logic To: Yosry Ahmed Cc: Takero Funaki , Johannes Weiner , Chengming Zhou , Jonathan Corbet , Andrew Morton , Domenico Cerasuolo , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: knzirxz5irfiowrxm6d74wuq9jaxaet7 X-Rspamd-Queue-Id: DF3E8C000A X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1718129716-800967 X-HE-Meta: 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 1NvklqIF sQyk9UGrWoGz2vUtDIvdtkks1yU90k9SEVkoS0AO2lhkitIZ3upw6DUczWdEYkfLezcGLmffaGEJsmN9VFPhBWO1G0YSqZYq/LS3rH7ViIZ/7tU+TvcwvmjgH5ErZUajqtA/ZXy7cMyGwsxGVGZq73tpWZGzHVwh/uuVhtbfc1+/vn1zfXUinLc4F95nXBZ8j6YIACzbBzZnHupQzGhMX86BKKmPl0KBcEVYLZNTCXRzCSXEwmXzsoe9LboAFhUO0AOXlOAc1M2nr9Eg+mL3Kx+NKBVz42RxYnZ7QHsbIdRK+/49sw92XGdinuw== 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 Mon, Jun 10, 2024 at 1:28=E2=80=AFPM Yosry Ahmed = wrote: > > On Sat, Jun 8, 2024 at 8:53=E2=80=AFAM Takero Funaki wrote: > > > > This patch fixes zswap global shrinker that did not shrink zpool as > > expected. > > > > The issue it addresses is that `shrink_worker()` did not distinguish > > between unexpected errors and expected error codes that should be > > skipped, such as when there is no stored page in a memcg. This led to > > the shrinking process being aborted on the expected error codes. > > > > The shrinker should ignore these cases and skip to the next memcg. > > However, skipping all memcgs presents another problem. To address this= , > > this patch tracks progress while walking the memcg tree and checks for > > progress once the tree walk is completed. > > > > To handle the empty memcg case, the helper function `shrink_memcg()` is > > modified to check if the memcg is empty and then return -ENOENT. > > > > Fixes: a65b0e7607cc ("zswap: make shrinking memcg-aware") > > Signed-off-by: Takero Funaki > > --- > > mm/zswap.c | 31 ++++++++++++++++++++++++++----- > > 1 file changed, 26 insertions(+), 5 deletions(-) > > > > diff --git a/mm/zswap.c b/mm/zswap.c > > index d720a42069b6..1a90f434f247 100644 > > --- a/mm/zswap.c > > +++ b/mm/zswap.c > > @@ -1393,7 +1393,7 @@ static struct shrinker *zswap_alloc_shrinker(void= ) > > > > static int shrink_memcg(struct mem_cgroup *memcg) > > { > > - int nid, shrunk =3D 0; > > + int nid, shrunk =3D 0, stored =3D 0; > > > > if (!mem_cgroup_zswap_writeback_enabled(memcg)) > > return -EINVAL; > > @@ -1408,9 +1408,16 @@ static int shrink_memcg(struct mem_cgroup *memcg= ) > > for_each_node_state(nid, N_NORMAL_MEMORY) { > > unsigned long nr_to_walk =3D 1; > > > > + if (!list_lru_count_one(&zswap_list_lru, nid, memcg)) > > + continue; > > + ++stored; > > shrunk +=3D list_lru_walk_one(&zswap_list_lru, nid, mem= cg, > > &shrink_memcg_cb, NULL, &nr= _to_walk); > > } > > + > > + if (!stored) > > + return -ENOENT; > > + > > Can't we just check nr_to_walk here and return -ENOENT if it remains as 1= ? > > Something like: > > if (nr_to_walk) > return -ENOENT; > if (!shrunk) > return -EAGAIN; > return 0; > > > return shrunk ? 0 : -EAGAIN; > > } > > > > @@ -1418,12 +1425,18 @@ static void shrink_worker(struct work_struct *w= ) > > { > > struct mem_cgroup *memcg =3D NULL; > > struct mem_cgroup *next_memcg; > > - int ret, failures =3D 0; > > + int ret, failures =3D 0, progress; > > unsigned long thr; > > > > /* Reclaim down to the accept threshold */ > > thr =3D zswap_accept_thr_pages(); > > > > + /* > > + * We might start from the last memcg. > > + * That is not a failure. > > + */ > > + progress =3D 1; > > + > > /* global reclaim will select cgroup in a round-robin fashion. > > * > > * We save iteration cursor memcg into zswap_next_shrink, > > @@ -1461,9 +1474,12 @@ static void shrink_worker(struct work_struct *w) > > */ > > if (!memcg) { > > spin_unlock(&zswap_shrink_lock); > > - if (++failures =3D=3D MAX_RECLAIM_RETRIES) > > + > > + /* tree walk completed but no progress */ > > + if (!progress && ++failures =3D=3D MAX_RECLAIM_= RETRIES) > > break; > > It seems like we may keep iterating the entire hierarchy a lot of > times as long as we are making any type of progress. This doesn't seem > right. > Ah actually, reading your comment closer then yeah the shrink-until-accept is the intended-ish behavior (from Domenico's older patches to re-work zswap reclaim). The one-page-per-attempt is also "intended" behavior, but not any of our's intentions - just something that remains from the past implementation as we rework this codebase one change at a time :)