Re: noatime on ufs2

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,
>