Date: Tue, 9 Jan 2024 07:21:29 +0900 From: Tomoaki AOKI <junchoon@dec.sakura.ne.jp> To: Warner Losh <imp@bsdimp.com> Cc: Xin LI <delphij@gmail.com>, freebsd-current@freebsd.org Subject: Re: noatime on ufs2 Message-ID: <20240109072129.3e6411b51a2f32945f41decd@dec.sakura.ne.jp> In-Reply-To: <CANCZdfpf0k4od%2B1_cNDiKR=HPwMZ0GsWhH9O6yRi=F72BwJRDg@mail.gmail.com> References: <ZZqmmM-6f606bLJx@int21h> <CAGMYy3vsSD7HHtGxYXJn%2Busr8GCOd-0Xe1crs-Nx=qw-bYJ6HA@mail.gmail.com> <CANCZdfpf0k4od%2B1_cNDiKR=HPwMZ0GsWhH9O6yRi=F72BwJRDg@mail.gmail.com>
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On Mon, 8 Jan 2024 14:12:06 -0700 Warner Losh <imp@bsdimp.com> wrote: > On Mon, Jan 8, 2024 at 1:41 PM Xin LI <delphij@gmail.com> wrote: > > > > > > > On Sun, Jan 7, 2024 at 5:27 AM void <void@f-m.fm> wrote: > > > >> Hi, > >> > >> Does /var/mail still need atime? > >> > >> I've installed a ufs2-based -current main-n267425-aa1223ac3afc on > >> rpi4/8BG which installs into one / . If it's mounted with noatime, > >> will it have consequences for /var/mail ? > > > > > > It doesn't matter if you don't normally receive emails locally (nowadays, > > it's rare). > > > > If you do receive emails locally, it depends on what application(s) that > > you are using. Most applications nowadays check both mtime and atime plus > > sizes of the mailbox file and do not rely on atime (because they saved the > > previous mtime). Without atime updates, some application may claim that > > you have new mail when the mailbox is not empty when they first start. > > > > That's said, if I were you and I'm using some flash based storage (with > > rpi it's highly likely) regardless if I'm using mail locally; most of the > > time the data is not really useful for anything, and it does increase the > > wear of your storage. > > > > This reminds me that -- we probably should have implemented the Linux > > "relative atime" (update atime iff (atime <= mtime || atime <= ctime) || > > atime is older than a day) and "no diratime" (don't update directory atime) > > for UFS and make the "relatime" option the default; I had an > > incomplete implementation about a decade ago somewhere but with the recent > > VFS changes it's probably easier to start over. IMHO, updating atime every > > time when a file is accessed is not really providing useful data (like who > > accessed the file, etc.) for audit purposes and does come with performance > > (more write I/O) and reliability (wear of SSD and other flash devices) > > cost, therefore not generally useful in modern days. The Linux relative > > atime is a pretty clever idea that has covered the most useful use case for > > atime (Did I accessed the file after it was last modified) and also > > provided a coarse-grained update (capped to daily, which is a reasonable > > compromise) to the atime. > > > > I like that compromise. It will miss a lot, but that 'miss' results in > atime being good to only about a day, which for the vast majority of things > is fine. > > Warner > > > > Cheers, Looks great if possible. Maybe /usr/bin/mail would be almost all of the MUA which actually require atime and local mailboxes (under /var/mail) would usually be used for local cron-generated ones. Others would use POP or IMAP running on different computer in most cases, I think. Regards. -- Tomoaki AOKI <junchoon@dec.sakura.ne.jp>
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