As I said, In the future vmcp will make use of the CMA allocator, which should make sure that the allocation will succeed. The advantage of that allocator is that this memory is not kept free, but it can be used by movable pages. So if vmcp needs that memory, CMA will be able to move that memory away and free up the necessary contigous space.
FWIW, you can actually make sure that vmcp will succeed _today_ as long as you keep the buffer size small enough. So as long as the buffer size is <= 2^3 pages (32kbytes) things should always work. So if you do vmcp inside a script or application you could split your queries into smaller chunks and avoid the fragmentation issue, e.g. instead of doing Q 0000-ffff do q 0000-07ff q 0800-0fff q 1000-17ff q 1800-1fff q 2000-2fff ... I am aware of at least one case where we fixed that as such in an IBM product, but I can not remember which one it was. Christian On 10/19/2017 08:27 AM, Pavelka, Tomas wrote: > Would it be possible for the vmcp kernel driver to have an option to > pre-allocate some fixed size of contiguous memory and hold onto it? This > would prevent fragmentation which can hit you at any time. I remember using > vmcp from a Linux based installer which typically started by downloading > large files over scp. Somehow scp caused a lot of fragmentation which made > fragmentation errors very likely. > If you have an application that runs a large number of vmcp commands, then > failed vmcp due to fragmentation means the end, because AFAIK there is no > sure way how to defragment, other than wait an unspecified amount of time. > > Tomas > > ---------------------------------------------------------------------- > 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/
