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Sun, 24 Dec 2023 13:26:16 -0800 (PST) Date: Sun, 24 Dec 2023 13:26:15 -0800 (PST) From: David Rientjes To: Pasha Tatashin cc: gregkh@linuxfoundation.org, rafael@kernel.org, akpm@linux-foundation.org, surenb@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, souravpanda@google.com Subject: Re: [PATCH] vmstat: don't auto expand the sysfs files In-Reply-To: Message-ID: References: <20231211154644.4103495-1-pasha.tatashin@soleen.com> <3d415ab4-e8c7-7e72-0379-952370612bdd@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 65096C0002 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: wau3up5hmgxucwiqr887m9wzaecxx86p X-HE-Tag: 1703453178-715304 X-HE-Meta: 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 y/TITkLe wGvNCYG03tIhJC8AsFy7AKQRKWHoHSwCMCDfeysUAXbQDlxigViYPSZOeigDUGu8MXCh0Oomvel8ryJUNGDRshbP/TvhKS68of+ww+3k4zHs/KtvjZhGqTbMY3khieMbb3VYFq3j08ul9bSgzHx8KaBSzUo9NLmWDqm5ho1FiUf0WDHusRWOkDktQC1GvQNC+zglXSPB18QftX+dsK6Cif0sm3Jjje6BXYDUWa1RPpVwzFBXCvk1/0oEbzlyffxg4yVKAB+djj99hcjI0vMTyjgz7aS0DilSfkZg8x58Or0EWF5mKWZ3BvISER9S1NUPGMlgTvwpE2JMVINu9+N/j18TH54qmPkArFGFW2PylUKr8/kyhSPIxTK96Ve4ajBTA6Eki+ZRKCTlsb5AXb5Tj5BY7oQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.013077, 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 Thu, 14 Dec 2023, Pasha Tatashin wrote: > > > Whenever a new fields are added one of the following: node_stat_item > > > numa_stat_item zone_stat_item, the /sys/devices/system/node/nodeX/vmstat > > > files are auto expanded. > > > > > > This is a problem, as sysfs files should be only one value per file. > > > > Does this patch address the one-value-per-file issue? (I think that ship > > has sailed for vmstat.) > > That ship has sailed for vmstat, this patch addresses what was asked > by GregKH: not to add new values to vmstat, as not to make the > existing problem even worse. The sysfs file system has a one page > limit per file. The developers will decide how to export the new items > added to node_stat, numa_stat, zone_stat individually. Each new item > can be exported in its own files, and must have its own documentation > about interface stability, value meaning, and expectations when the > stat file is absent. > As of at least 6.5, /proc/vmstat is a strict superset of the per-node vmstat. Why is that a problem? There's great benefit to being able to use the sample implementations to parse either /proc/vmstat *or* the per-node vmstat and without needing to read the per-node vmstat plus some new set of sysfs files that are one-value-per-file. The per-node vmstat will always be multiple values, in fact it's a key value pair. I have to think that doing anything else for vmstat is just adding complexity (like this patch) and actually making it *harder* on userspace to read the data it needs. Yes, the per-node vmstat likely shouldn't be in sysfs at all but it appears to have been added there 13+ years ago because it was a convenient place to add a per-node variant. That's not ideal, but owell.