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Mon, 13 Mar 2023 13:26:44 -0300 (-03) Message-ID: <20230313162507.032200398@redhat.com> User-Agent: quilt/0.67 Date: Mon, 13 Mar 2023 13:25:07 -0300 From: Marcelo Tosatti To: Christoph Lameter Cc: Aaron Tomlin , Frederic Weisbecker , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Russell King , Huacai Chen , Heiko Carstens , x86@kernel.org, Vlastimil Babka Subject: [PATCH v5 00/12] fold per-CPU vmstats remotely X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 3641C14001A X-Stat-Signature: y1w7c7yz8e15fsky6iyerq76nius1z1o X-HE-Tag: 1678724866-202808 X-HE-Meta: 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 JiNh51qj u09x1oyBpMrVb68mLsfaL57o9MhHaJvOTyNHEzPaw7Q6aKNoASQ9z/tBSVXJdmJ0vIVNiIWFfrtkYIwR5s0jnTZ9jWFu56m6L0qsNk/umaxkvfa9D4KES6B+Vpt5XyKXDj31b 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: This patch series addresses the following two problems: 1. A customer provided some evidence which indicates that the idle tick was stopped; albeit, CPU-specific vmstat counters still remained populated. Thus one can only assume quiet_vmstat() was not invoked on return to the idle loop. If I understand correctly, I suspect this divergence might erroneously prevent a reclaim attempt by kswapd. If the number of zone specific free pages are below their per-cpu drift value then zone_page_state_snapshot() is used to compute a more accurate view of the aforementioned statistic. Thus any task blocked on the NUMA node specific pfmemalloc_wait queue will be unable to make significant progress via direct reclaim unless it is killed after being woken up by kswapd (see throttle_direct_reclaim()) 2. With a SCHED_FIFO task that busy loops on a given CPU, and kworker for that CPU at SCHED_OTHER priority, queuing work to sync per-vmstats will either cause that work to never execute, or stalld (i.e. stall daemon) boosts kworker priority which causes a latency violation By having vmstat_shepherd flush the per-CPU counters to the global counters from remote CPUs. This is done using cmpxchg to manipulate the counters, both CPU locally (via the account functions), and remotely (via cpu_vm_stats_fold). Thanks to Aaron Tomlin for diagnosing issue 1 and writing the initial patch series. v5: - Drop "mm/vmstat: remove remote node draining" (Vlastimil Babka) - Implement remote node draining for cpu_vm_stats_fold (Vlastimil Babka) v4: - Switch per-CPU vmstat counters to s32, required by RISC-V, ARC architectures v3: - Removed unused drain_zone_pages and changes variable (David Hildenbrand) - Use xchg instead of cmpxchg in refresh_cpu_vm_stats (Peter Xu) - Add drain_all_pages to vmstat_refresh to make stats more accurate (Peter Xu) - Improve changelog of "mm/vmstat: switch counter modification to cmpxchg" (Peter Xu / David) - Improve changelog of "mm/vmstat: remove remote node draining" (David Hildenbrand) v2: - actually use LOCK CMPXCHG on counter mod/inc/dec functions (Christoph Lameter) - use try_cmpxchg for cmpxchg loops (Uros Bizjak / Matthew Wilcox) arch/arm64/include/asm/percpu.h | 16 ++ arch/loongarch/include/asm/percpu.h | 23 +++- arch/s390/include/asm/percpu.h | 5 arch/x86/include/asm/percpu.h | 39 +++---- include/asm-generic/percpu.h | 17 +++ include/linux/mmzone.h | 3 include/linux/percpu-defs.h | 2 kernel/fork.c | 2 kernel/scs.c | 2 mm/page_alloc.c | 23 ---- mm/vmstat.c | 424 +++++++++++++++++++++++++++++++++++++++++------------------------------------ 11 files changed, 307 insertions(+), 249 deletions(-)