I have to agree with Mark. From the beginning, the goal was to keep Linux from swapping, and allow zVM to page if necessary. There¹s no sense in two different layers virtualizing memory. If you¹re pushing into swap, consider making the virtual machine bigger.
zVM can easily handle a 2:1 overallocation of memory, and paging rates in the thousands per second. There¹s no reason to have Linux paging or swapping, let alone wasting resources compressing the swap. -- Robert P. Nix | Sr IT Systems Engineer | Data Center Infrastructure Services Mayo Clinic | 200 First Street SW | Rochester, MN 55905 507-284-0844 | [email protected] "quando omni flunkus moritati" On 3/10/16, 1:45 PM, "Linux on 390 Port on behalf of Mark Post" <[email protected] on behalf of [email protected]> wrote: >>>> On 3/10/2016 at 01:25 PM, Christer Solskogen >>>><[email protected]> >wrote: >> This is a bit more technical: https://lwn.net/Articles/537422/ > >Based on the lead-in to the article, this was intended for systems where >CPU and RAM are cheap, and I/O is very expensive. For the mainframe, >neither CPU nor RAM are cheap, but the I/O is quite a bit less expensive >than on other architectures. I suppose support for the zEDC hardware >compression feature would reduce some of the CPU expended for compression. > >> I wouldn't say experimental anymore, since it's been in the kernel >>since >> 3.7. > >The kernel developers themselves have flagged it that way: >Compressed cache for swap pages (EXPERIMENTAL) > >> The reason I'm asking is that on x86_64 is enabled on Ubuntu like this: >> CONFIG_ZSWAP=y >> >> While on SLES11 and SLES12 on s390x CONFIG_ZSWAP isn't even mentioned, >> so at first it didn't even look like ZSWAP is available at all on >> s390x. >> If the module was available, but not compiled in it would look >> something like this: #CONFIG_ZSWAP is not set > >Since this was introduced with 3.7, it would only be available on SLES11 >if there had been a feature request to back port it to the 3.0.101 kernel >in use. > >The ZSWAP feature depends on FRONTSWAP being configured. For SLES12, we >don't enable the FRONTSWAP feature on s390x, which means that the ZSWAP >feature isn't even presented as an option. The fact that both FRONTSWAP >and ZSWAP are configured on x86_64 tells me that there was a conscious >decision made to exclude it on s390x. If you believe you have a business >need for this feature, you should talk to your sales rep. or technical >sales support rep. to get a feature request entered for that. > > >Mark Post > >---------------------------------------------------------------------- >For LINUX-390 subscribe / signoff / archive access instructions, >send email to [email protected] with the message: INFO LINUX-390 or >visit >http://www.marist.edu/htbin/wlvindex?LINUX-390 >---------------------------------------------------------------------- >For more information on Linux on System z, visit >http://wiki.linuxvm.org/ > ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
