Hello everyone, On Wed, Jan 05, 2011 at 08:44:38PM +0100, Alexander Graf wrote: > > On 05.01.2011, at 19:02, Michael Roth wrote: > > > On 01/05/2011 09:10 AM, Andrea Arcangeli wrote: > >> The bug is still there so I rediffed the old patch against current > >> code. > >> > >> On a related topic: could somebody give me advice on how to implement > >> a command line (command line seems enough, the other option would be > >> monitor command) to make the MADV_MERGEABLE conditional? I got KSM on > >> THP working fine but KSM may decrease performance by increasing the > >> number of copy on write and by splitting hugepages, so we'd like to be > >> able to turn off KSM on a per-VM basis (not on the whole host, which > >> of course we already can by setting /sys/kernel/mm/ksm/run to 0) so > >> that high perf VMs will keep running at maximum speed with KSM off but > >> others may still benefit from KSM. For that I need to make the below > >> MADV_MERGEABLE madvise conditional to something and the code itself > >> will be trivial, we've just to converge on a command line option > >> (hopefully quickly ;). > > > > There was a -mem_prealloc option added a while back to set MAP_POPULATE on > > memory mapped in via the -mem-path option. So an analogous -mem_nomerge > > option or something along that line seems reasonable for conditionally > > unsetting QEMU_MADV_MERGEABLE. > > > > And for consistency you should probably make both your proposed changes for > > -mem-path'd memory as well. > > Why not clean up all that mess and introduce a new -mem option that would > just take all of the several options as parameters? > > -mem size=512,populate=on,ksm=off > > and default -m to something reasonable with the new syntax.
I'm neutral... so feel free to decide what I should implement ;). One comment on combining -m ksm=off (or -mem_nomerge) with -mem-path. It seems unnecessary because ksm can't be turned on on VM_HUGETLB vmas (MADV_MERGEABLE will return -EINVAL) and mem-path only makes sense if used in combination with hugetlbfs (which sets VM_HUGETLB of course).