PS Swap Memory suggestion accepted - Wow!

This is so cool, I am so exited:

I had made a suggestion to double swap memory to twice the amount of RAM for PS servers. I never saw it in the items to vote on, but today I found that it's already in the list of "suggestions we are working on"!!!

In reply to:

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2009-05-26 DreamHost PS Double Dreamhost PS swap memory to twice the amount of RAM 3 credits
in progress This suggestion has been forwarded to the Dreamhost development team for implementation.

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My description was:

In reply to:

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Swap memory on PS servers is needlessly limited and much lower than on shared servers. The result is that sites are not fully burstable. I get more "500 server errors" due to sudden peaks on my PS than I did on my shared server, in spite of paying 30$ to 35$ dollars more per month!!!

By increasing swap memory to be twice the amount of actual RAM this
problem might be eliminated and sites can be truly burstable. Ex: for 600
MB of RAM, the swap should be 1200 MB. Currently it would be limited to
450 MB.

The price of RAM on DH is relatively high, and I believe we should at
least get something in return for that that is able to fully handle sudden
traffic peaks.

Alternatively I would also be happy with being allowed to set our own swap
memory level.

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Apparently Dreamhost liked this idea enough that they are just going to implement it without waiting for it to get votes!!! What can I say, I just love Dreamhost!

Otto - 7is7.com

Great idea !

Thanks.

I've just switched to PS. It is great!

I'll be checking the swap memory everyday. Let's see when it is going to happen

Just wonder how great is it ? Because I have several invitations.

Regards

Supernova

I'm not a system administrator and I could not tell you what is exactly good about private server. But when my site was located in shared server, the load average went up to 50 or 60 for some reasons.

After my site was moved to private server, the load average is below 1 now.

If a server has 3G memory, I would assume there are maximum 20 users on the same server because the minimum guaranteed memory in private server is 150MB per user. This is my own calculation. It could be wrong or misleading. But I am very happy with the load average right now.

No news about higher swap memory ?

Thanks !

At least not for me yet. My swap memory size is still same as memory size.

For me neither.
No idea when it will be implemented or how it will be rolled out.
I guess it's something we might read in an upcoming newsletter.

Otto - 7is7.com

Sorry to burst your bubble, but the fact that your suggestion got marked as "accepted" is the result of a bug.

For some reason, about half of the users who screened this suggestion selected the option that "this suggestion is really easy or a bug fix". I'm not sure why they picked this (because it's neither easy nor a bug fix), but this ended up kicking it into the "accept automatically" bin.

Moreover, it's a little unclear to me what the suggestion is actually asking for. While we do display an amount of "swap" memory for PS customers, this doesn't actually correspond directly to swap space on the host. There are some details on http://linux-vserver.org/Memory_Limits if you're interested - but the gist of it is that "swap" represents memory which your processes can use, but aren't guaranteed to have available.

Again, this is a bug: we aren't actually working on this feature. I've just gone ahead and forced it back into voting, but I can't make any guarantees about whether it's something we can or will implement if it's accepted.

That's all very strange, because the suggestion is still listed in the category "Suggestions we are working on".

I also have to correct a few statements you made:

> I'm not sure why they picked this (because it's neither easy nor a bug fix)

It's is EXTREMELY easy to fix, because it's just a setting. It's only a matter of deciding to actually do it.

> but the gist of it is that "swap" represents memory which your processes can use, but aren't guaranteed to have available.

The swap memory we are talking about is memory that is written to disc if you run out of RAM. You can read more about it here:
http://linux.com/news/software/applications/8208-all-about-linux-swap-space
It's always available (as long as you have available disc space to write to, which you can guarantee).

Dreamhost is keeping swap memory on the low side. Someone who uses 2 GB of RAM on their VPS only gets 450 MB of Swap memory.

Contrast this with my current workstation at home. I have 2 GB of RAM and 4 GB of Swap space. Also contrast this with a friend of mine who has a VPS at slicehost, his Swap space is double his RAM (and he pays less per MB of RAM than we do). And finally contrast that withthe shared servers at Dreamhost, they are running on systems that have 4 GB of RAM and 6 GB of Swap space (and those users don't even pay for the RAM).

It seems to me only fair that we get more Swap space on our VPS too, keeping it so low can cause "500" server errors, totally needlessly as it would be really easy to use swap space for it. And as a result our sites aren't really burstable at all as Dreamhost claims.

I hope this clarifies the issue for you, and I hope Dreamhost changes this quickly.

Otto - 7is7.com

> That's all very strange, because the suggestion is still listed in the category "Suggestions we are working on".

I've corrected this. Thanks for pointing it out.

The suggestion is now open for voting at: https://panel.dreamhost.com/index.cgi?tree=home.sugg&category=_all&search=PS+swap

> It's is EXTREMELY easy to fix, because it's just a setting. It's only a matter of deciding to actually do it.

This is simply not the case. While changing the numbers is easy enough, ensuring that this will not negatively impact the stability of existing PS hosts is difficult.

> The swap memory we are talking about is memory that is written to disc if you run out of RAM. You can read more about it here...

I'm quite aware of how swap works under Linux. However, as noted in the link I attached to my previous post, the meaning of "swap" under Linux VServers is different from what it means under physical hardware. While the host machine does have swap space available, it isn't directly exposed to the guests.

Really, we'd prefer you didn't think of it as swap space at all. Think of it as a bit of bonus memory you can use in emergencies.

> It seems to me only fair that we get more Swap space on our VPS too, keeping it so low can cause "500" server errors, totally needlessly as it would be really easy to use swap space for it. And as a result our sites aren't really burstable at all as Dreamhost claims.

If your site needs more memory than you currently have allocated, allocate more. Burstable memory ("swap") is not a substitute for increasing your allocation - in fact, running processes in burstable memory will increase the number of 500 errors you get, as processes running in burstable memory are killed first in low-memory situations.

> If your site needs more memory than you currently have allocated, allocate more. Burstable memory ("swap") is not a substitute for increasing your allocation - in fact, running processes in burstable memory will increase the number of 500 errors you get, as processes running in burstable memory are killed first in low-memory situations.

So basically you are saying that people need to allocate more memory to be burstable. I was not talking running process in swap memory all the time, but about being able to deal with the bursts that occasionally happen. And I for one want my swap to be able to deal with that. I don't want to reserve 3 times more memory than I need 99% of the time for the few occasions that there is a short lasting spike in memory usage.

> I'm quite aware of how swap works under Linux. However, as noted in the link I attached to my previous post, the meaning of "swap" under Linux VServers is different from what it means under physical hardware. While the host machine does have swap space available, it isn't directly exposed to the guests.

What I understood from your link is that the memory allocated to us may be either RAM or disk swap memory, because both are put together and distributed to the virtual servers. So say if your machine has 4000 MB and the machine has 6000 MB swap (as your shared hosts do), the virtual servers' base memory that may actually already be swap memory (at least physically). And theoretically at least we may be paying for physical swap memory as if it's real memory. I guess it all depends of how it's set up. But it seems to me that if your physical machine has 4000 MB Ram and 6000 MB disk swap then you should be distributing the physical swap memory as available swap memory to the virtual servers and certainly not as main memory. And even though it may be more complicated than that at least the proportions should then match imo.


Otto - 7is7.com

Today I noticed my PS memory at 716 MB with swap at 900 MB, so something has changed. My logs show that the swap is set to twice the memory with a maximum of 900 MB, since yesterday.

Otto - 7is7.com

Any updates?

FWIW allocating high amounts of swap on shared servers, which VPSs are, imposes a high network/disk overhead.

Remember you are swapping out over a network or a Fibre Channel interface you are sharing with others, not directly over a SATA or SCSI interafce.

You should be barely if at all be hitting your swap. If you hit your swap every once in a blue moon that's nothing to worry about. But if you're hitting it regularly you should first review your scripts or increase your memory.

"The surest way to corrupt a youth is to instruct him to hold in higher esteem those who think alike than those who think differently."
-- Friedrich Nietzsche