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Fri, 21 Apr 2023 11:55:03 -0700 (PDT) MIME-Version: 1.0 References: <20230421174020.2994750-1-yosryahmed@google.com> In-Reply-To: <20230421174020.2994750-1-yosryahmed@google.com> From: Yosry Ahmed Date: Fri, 21 Apr 2023 11:54:25 -0700 Message-ID: Subject: Re: [PATCH v5 0/5] cgroup: eliminate atomic rstat flushing To: Alexander Viro , Christian Brauner , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Tejun Heo Cc: Jan Kara , Jens Axboe , =?UTF-8?Q?Michal_Koutn=C3=BD?= , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 9F23D140014 X-Stat-Signature: 8f4zjcyz8rzhr9gs3sxwb5copp1w14p4 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1682103305-373691 X-HE-Meta: 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 sVFwulCO qvXu8FqFeRf0SoJz1fJzjpPJkAvfWAr5103a+b2BPGPH9ogPOfpgudPbh3JGcoZK+g/pX73JNNryUp7WwT7dJZk32xeoxACPFz+O9+OusPR6OGZtvrXJN/oSMb62aWOhPm1k1zASsz/oh+lxJu7vrv0Hc9j11rZwDdzqf2M0K7pNmCliTLlN2O/5bl0LbelP01DEWcHnmmpgcjhMgl+H7nqgMdUkVTqLs6qw8FK8RGOBKjpPDT2ZGJsn0XwI7Aldi3S86Dg5bqioAfkjZmH2PfEyOzrWIALViqPPkpo/rqtZY2Ut1yJbYCBZ3EQ== 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 Fri, Apr 21, 2023 at 10:40=E2=80=AFAM Yosry Ahmed wrote: > > A previous patch series ([1] currently in mm-stable) changed most > atomic rstat flushing contexts to become non-atomic. This was done to > avoid an expensive operation that scales with # cgroups and # cpus to > happen with irqs disabled and scheduling not permitted. There were two > remaining atomic flushing contexts after that series. This series tries > to eliminate them as well, eliminating atomic rstat flushing completely. > > The two remaining atomic flushing contexts are: > (a) wb_over_bg_thresh()->mem_cgroup_wb_stats() > (b) mem_cgroup_threshold()->mem_cgroup_usage() > > For (a), flushing needs to be atomic as wb_writeback() calls > wb_over_bg_thresh() with a spinlock held. However, it seems like the > call to wb_over_bg_thresh() doesn't need to be protected by that > spinlock, so this series proposes a refactoring that moves the call > outside the lock criticial section and makes the stats flushing > in mem_cgroup_wb_stats() non-atomic. > > For (b), flushing needs to be atomic as mem_cgroup_threshold() is called > with irqs disabled. We only flush the stats when calculating the root > usage, as it is approximated as the sum of some memcg stats (file, anon, > and optionally swap) instead of the conventional page counter. This > series proposes changing this calculation to use the global stats > instead, eliminating the need for a memcg stat flush. > > After these 2 contexts are eliminated, we no longer need > mem_cgroup_flush_stats_atomic() or cgroup_rstat_flush_atomic(). We can > remove them and simplify the code. > > [1] https://lore.kernel.org/linux-mm/20230330191801.1967435-1-yosryahmed@= google.com/ > > RFC -> v1: > - Collected R-b's and A-b's (Thanks everyone!). > - Rebased onto mm-stable. > - Cosmetic changes to commit logs. > > RFC: https://lore.kernel.org/linux-mm/20230403220337.443510-1-yosryahmed@= google.com/ This is v1, not v5. I really suck at sending emails. Sorry. > > Yosry Ahmed (5): > writeback: move wb_over_bg_thresh() call outside lock section > memcg: flush stats non-atomically in mem_cgroup_wb_stats() > memcg: calculate root usage from global state > memcg: remove mem_cgroup_flush_stats_atomic() > cgroup: remove cgroup_rstat_flush_atomic() > > fs/fs-writeback.c | 16 +++++++---- > include/linux/cgroup.h | 1 - > include/linux/memcontrol.h | 5 ---- > kernel/cgroup/rstat.c | 26 ++++-------------- > mm/memcontrol.c | 54 ++++++++------------------------------ > 5 files changed, 27 insertions(+), 75 deletions(-) > > -- > 2.40.0.634.g4ca3ef3211-goog >