[DragonFlyBSD - Bug #2868] tmpfs problems: incorrect size, no auto-size

bugtracker-admin at leaf.dragonflybsd.org bugtracker-admin at leaf.dragonflybsd.org
Sun Dec 20 12:25:47 PST 2015

Issue #2868 has been updated by arcade at b1t.name.

Actually `mount_tmpfs`(8) says:

     -s size     Specifies the total file system size.  If zero is given (the
                 default), the available amount of memory (including main
                 memory and swap space) will be used.  Note that four
                 megabytes are always reserved for the system and cannot be
                 assigned to the file system.

There's nothing in here limiting tmpfs size down to 200k on a system with 1G mem or down to 30G on a system with 56G swap.

On FreeBSD... In FreeBSD each tmpfs size equals 'used space' + 'available_space' so that capacity of mounted tmpfs by default depletes when swap and memory are fully used up. Dunno whether this is hard to achieve but it makes single simple line in fstab useful in most conditions.

PS: And mentioning that FreeBSD version can be superior... For example in 2013 they replaced linked lists for directory structures with RB-Tree.

PPS: I'm not talking about blindly copying everything from FreeBSD. I'm just pointing out "weird" defaults not clarified by man pages. From my point of view tmpfs is a vital addition to hammer.

Bug #2868: tmpfs problems: incorrect size, no auto-size

* Author: arcade at b1t.name
* Status: New
* Priority: Low
* Assignee: 
* Category: VFS subsystem
* Target version: 
tmpfs version in DragonFly is limited  when comparing to FreeBSD:

1. When tmpfs is mounted automatically it's size by default (per man page) should be equal to all free mem + all free swap. Instead tmpfs filesystems are created with a fairly small size - like 200k on host with 1G mem.
2. tmpfs size should be auto adjusted when other processes are eating mem or when swap is added. Instead as swap is initialized after mounting /tmp swap addition doesn't make tmpfs grow. On the other hand I never saw tmpfs shrinking when all available memory is used.

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