Thanks Brian for the explanation. :)

On Wed, Feb 3, 2010 at 4:26 PM, Brian Ruthven - Solaris Network
Sustaining - Sun UK <[email protected]> wrote:
>
> tmpfs and ufs/zfs are different things.
>
> You limit the amount of "swap" (i.e. disk-backed 'memory') by varying the
> size of the device added using "swap -a", or the lines in vfstab with 'swap'
> in the "FS type" column. This is the "memory" available to all processes.
>
> You limit the amount of swap use by tmpfs by using the "size=" mount option
> or the options column of the /tmp line in vfstab (which has an FS type of
> tmpfs, not swap).
>
> Whilst I can't demonstrate re-mounting /tmp with the size= option, I can
> mount a new filesystem from swap in the same way whilst using zfs root:
>
> # mount -Ftmpfs swap /a
> # df -h /a
> Filesystem            Size  Used Avail Use% Mounted on
> swap                  704M     0  704M   0% /a
> # umount /a
> # mount -Ftmpfs -osize=100m swap /a
> # df -h /a
> Filesystem            Size  Used Avail Use% Mounted on
> swap                  100M     0  100M   0% /a
>
>
> See mount_tmpfs(1M) for the full range of options for tmpfs mounting. These
> options are independent of your root filesystem type.
>
> If you're saying that with zfs root, setting "size=" on the tmpfs line of
> /etc/vfstab does not work, I would say a bug needs to be logged about it.
>
>
> Regards,
> Brian
>
>
>
> On 02/ 1/10 06:15 AM, Prakash Kochummen wrote:
>>
>> Hi,
>>
>> While using ufs root, we had an option for limiting the /tmp size using
>> mount -o size manual option or setting size=1024m in the vfstab.
>>
>> Do we have any comparable option available when we use zfs root. If we
>> execute
>> zfs set size=1024m rpool/swap
>> it resizes the whole of the swap area which results in reducing the VM
>> size.
>>
>> AFAIK in the ufs option for limiting swap size, we are just limiting the
>> filesystem behaviour of the tmpfs filesystem while the kernel will still be
>> able to use the swap space for paging etc. Is this correct understanding.
>>
>> Thanks in advance.
>>
>> Rgds
>> PK
>>
>
> --
> Brian Ruthven
> Solaris Revenue Product Engineering
> Sun Microsystems UK
> Sparc House, Guillemont Park, Camberley, GU17 9QG
>
>
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