[CentOS-docs] Contributing Wiki article on tmpfs

[Brian Mathis]

Looks good.  I appreciate the discussion on the priority of the RAM
space used and issues to think about as far as swap space size and
when it starts using disk.

One thing that concerns me in the tmpfs.txt file is this statement:
    If you oversize your tmpfs instances the machine will deadlock
    since the OOM handler will not be able to free that memory.
I assume that means you shouldn't allocate more to tmpfs than you have
physical memory, but I've also seen other sites suggesting to use
size=100% (vmware server tuning).  So far I think 100% would be fine,
just not 110%.  I'm not sure if you have any further insight into
that.

Anyway, thanks for taking the time to address my comments.


On Wed, Nov 4, 2009 at 4:19 PM, Jasper Siepkes <jasper at siepkes.nl> wrote:
> Hi,
>
> First of all sorry for the long delay and thanks for the constructive
> feedback.
>
> I've made some additions to the Wiki article
> ( http://wiki.centos.org/TipsAndTricks/TmpOnTmpfs ):
>
> -Added the 'Practical details' section to explain how tmpfs, swap and
> memory relate.
> -Added a 'Pitfalls' section to warn people of an (IMHO) somewhat
> misguided piece of advice in the official documentation and maybe some
> other pitfalls when I think of them.
>
> About ramdisks; I will add something later about how tmpfs relates to
> other ramdisk implementations like cramfs and squashfs. But I haven't
> done much with the former two so I will need to research those a bit
> before I can write something down.
>
> I'm not the best writer on this continent (Shakespeare beat me by half a
> point, but I suspect foul play ;-) but I think I've made some steps in
> the right direction with the article. Please let me know what you think
> and where I should make some additional improvements.
>
> Regards,
>
> Jasper
>
> On Tue, 2009-10-20 at 14:38 -0400, Brian Mathis wrote:
>> On Tue, Oct 20, 2009 at 1:46 PM, Jasper Siepkes <jasper at siepkes.nl> wrote:
>> > Hi,
>> >
>> > I've made a first attempt at writing the tmpfs CentOS Tips and tricks item
>> > and I'm looking for some feedback. Does it need more (or less) background
>> > info ? Or more (or less) substance perhaps ?
>> >
>> > Regards,
>> > Jasper
>> >
>>
>> I'd like to see more info on things like:
>> - What is the relationship with swap?
>> - How/when does swap get used instead of RAM?
>> - How do I determine the size of RAM to use?
>> - What impact does using 100% of RAM have on the active memory in the system?
>> - What happens if all system RAM is full, and tmpfs is also full?
>>
>> I think your doc is a good start, but as of now it's got the same info
>> as all the other tmpfs docs out there, and they don't go into much
>> detail about the real impact on a system when using tmpfs.
>>
>> Tmpfs is billed as a more sophisticated ramdisk, so docs addressing it
>> should go into the details of what makes it better.  A simple ramdisk
>> just allocates a chunk of RAM, so why is tmpfs better?