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bh=6zfLpT7hdLdE3kG/mQnDxvbrMCXCopNqVUMzvG7Y9T8=; b=rsdLN5ilHTbzv21f1Wx+6gLpDof3nwrEUJLpwa2BEykTDXfcEjeij80pJ0spDrnUBvEKr8 iD6ObV48rgPH3qRLfFp29rsRTQupuy4EP19wyuq3JJRkdz3NbAsjVtovmCS7kxKKzuorro ekcXIZUL0/2sOCo/G63uA17f9QRAQGw= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id D602813A26; Tue, 14 Mar 2023 12:25:53 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id SftwM9FnEGRaVQAAMHmgww (envelope-from ); Tue, 14 Mar 2023 12:25:53 +0000 Date: Tue, 14 Mar 2023 13:25:53 +0100 From: Michal Hocko To: Marcelo Tosatti Cc: Christoph Lameter , 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: Re: [PATCH v5 00/12] fold per-CPU vmstats remotely Message-ID: References: <20230313162507.032200398@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230313162507.032200398@redhat.com> X-Rspamd-Queue-Id: 8DA6A4001E X-Stat-Signature: kmnfteytkmotsnp38tiwm7nopwzfua64 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1678796755-140787 X-HE-Meta: U2FsdGVkX19BjJS6HS/fHlYF5kovIvgdL2ru+67vCTqqnExr58AQcznk1ctnc3Qrgxzl5DIQoM6IHF3hg4GbGpjYssXvIwC4DyYTIgX5sqn/iDXlQnV9SHP7da5XGlBpgQ7Sqa8+a0141pAs9x9xJmt/0tSui5d0CgSDIj16mRbEvkeL6q095dt8rkAOHtmLMrIvYzgo2BHatnhIp8lXojEpUPbqPeNqHJiRCcoexIq6hwIB6NjGtAEwXsqLYSD8U337Wdt71QhBUqPwgd1XqJb9qukIj2rtBVdNZOX0lRBCpNREarDUcPs1ycaObw2HWO8OwHPEm7jSwjC6bC7qdAPv6O5KAIuBy+dtEaXMHpC2PBfUeJusP+V5iKNG5iFbs5KhRB/QrW7qYhMjmJIpG2m8OiKvsHxnS+GF9JneQEIDj6pVbf2PDJ1BOBmQ4Zd3gcYjQe+1lFmqxLLw1QxT3EoLrtrgoz29hG2SQQpR16gWeBWDUUWBUslyrLg58pMLP+1zSptA+Sk0hlZrZSJ4LBSl43h8W9y0AfVNXkm5jSN7nVdcyMe1VUzaU9bf2JX/iABSmdNGZ3WQRhH41SFTTfNe/l8UbLk5dkKzT8WZKlpWBgVdc/18gWZg0O0bU7dHXYOPhUkSh5S7zSAO7vsY6/wHbvKsqpYacnBrcmIUtFqvPmyCPtOWjPPkFBFvnIqiNesASpXyuKpU/6pPyF4m/WppgqyEZvw7fpeeyj4qjI6PP5+2LXYmtcjFqFUwwBTY+eI8pg5tvcYan7DAAMzp/AgWNMD+zZLAyCjLKJhtzWRF/uSZ3xlpIbIuqRzPpCN+HKW3/Tb8K6DUX8Qdo9215ZB4H4aAPzn91iaDtcmL35td2uHrXqgsjQE4SMQa0Dv8EYXthxF0W0DQC3wpLBSTTZxB4OMauMKbbtz1+cfF0lJiJlacZa6fZskKd5k7RPk3qRUZMucPOvQrYzU1n+Z OvHGpz5q lX9inX6YHfN3J38UDDr+I4SWbf7Du9ep++9ez13PYxGINbawbqkIh5l2qsOJAWvd/UzfHPkkRlwyWVHwFcCv061UWfuzwNY1EeXoTWwn0gsw2HWYYm4SLoky3sNQkhjgV0ge8S7sMcNmZcqs3ljfMT9teT/Wsw1U9Icl7EQBfrfFptBM= 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 Mon 13-03-23 13:25:07, Marcelo Tosatti wrote: > 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()) I have hard time to follow the actual problem described above. Are you suggesting that a lack of pcp vmstat counters update has led to reclaim issues? What is the said "evidence"? Could you share more of the story please? > 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 Why is that a problem? Out-of-sync stats shouldn't cause major problems. Or can they? Thanks! -- Michal Hocko SUSE Labs