[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [RFC PATCH qemu 0/4] memory: Reduce memory use
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [RFC PATCH qemu 0/4] memory: Reduce memory use |
Date: |
Thu, 7 Sep 2017 15:54:03 +0100 |
User-agent: |
Mutt/1.8.3 (2017-05-23) |
* Alexey Kardashevskiy (address@hidden) wrote:
> On 07/09/17 19:51, Dr. David Alan Gilbert wrote:
> > * Alexey Kardashevskiy (address@hidden) wrote:
> >> This was inspired by https://bugzilla.redhat.com/show_bug.cgi?id=1481593
> >>
> >> What happens ithere is that every virtio block device creates 2 address
> >> spaces - for modern config space (called "virtio-pci-cfg-as") and
> >> for busmaster (common pci thing, called after the device name,
> >> in my case "virtio-blk-pci").
> >>
> >> Each address_space_init() updates topology for every address space.
> >> Every topology update (address_space_update_topology()) creates a new
> >> dispatch tree - AddressSpaceDispatch with nodes (1KB) and
> >> sections (48KB) and destroys the old one.
> >>
> >> However the dispatch destructor is postponed via RCU which does not
> >> get a chance to execute until the machine is initialized but before
> >> we get there, memory is not returned to the pool, and this is a lot
> >> of memory which grows n^2.
> >>
> >> These patches are trying to address the memory use and boot time
> >> issues but tbh only the first one provides visible outcome.
> >
> > Do you have a feel for how much memory is saved?
>
>
> The 1/4 saves ~33GB (~44GB -> 11GB) for a 2GB guest and 400 virtio-pci
> devices. These GB figures are the peak values (but it does not matter for
> OOM killer), memory gets released in one go when RCU kicks in, it just
> happens too late.
Nice saving! Still, why is it using 11GB?
What's it like for more sane configurations, say 2-3 virtio devices - is
there anything noticable or is it just the huge setups?
Dave
> The 3/4 saves less, I'd say 50KB per VCPU (more if you count peaks but so
> much). Strangely, I do not see the difference in valgrind output when I run
> a guest with 1024 or just 8 CPUs, probably "massif" is not the right tool
> to catch this.
>
> >
> > Dave
> >
> >> There are still things to polish and double check the use of RCU,
> >> I'd like to get any feedback before proceeding - is this going
> >> the right way or way too ugly?
> >>
> >>
> >> This is based on sha1
> >> 1ab5eb4efb Peter Maydell "Update version for v2.10.0 release".
> >>
> >> Please comment. Thanks.
> >>
> >>
> >>
> >> Alexey Kardashevskiy (4):
> >> memory: Postpone flatview and dispatch tree building till all devices
> >> are added
> >> memory: Prepare for shared flat views
> >> memory: Share flat views and dispatch trees between address spaces
> >> memory: Add flat views to HMP "info mtree"
> >>
> >> include/exec/memory-internal.h | 6 +-
> >> include/exec/memory.h | 93 +++++++++----
> >> exec.c | 242 +++++++++++++++++++--------------
> >> hw/alpha/typhoon.c | 2 +-
> >> hw/dma/rc4030.c | 4 +-
> >> hw/i386/amd_iommu.c | 2 +-
> >> hw/i386/intel_iommu.c | 9 +-
> >> hw/intc/openpic_kvm.c | 2 +-
> >> hw/pci-host/apb.c | 2 +-
> >> hw/pci/pci.c | 3 +-
> >> hw/ppc/spapr_iommu.c | 4 +-
> >> hw/s390x/s390-pci-bus.c | 2 +-
> >> hw/vfio/common.c | 6 +-
> >> hw/virtio/vhost.c | 6 +-
> >> memory.c | 299
> >> +++++++++++++++++++++++++++--------------
> >> monitor.c | 3 +-
> >> vl.c | 4 +
> >> hmp-commands-info.hx | 7 +-
> >> 18 files changed, 448 insertions(+), 248 deletions(-)
> >>
> >> --
> >> 2.11.0
> >>
> >>
> > --
> > Dr. David Alan Gilbert / address@hidden / Manchester, UK
> >
>
>
> --
> Alexey
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [Qemu-devel] [RFC PATCH qemu 1/4] memory: Postpone flatview and dispatch tree building till all devices are added, (continued)
[Qemu-devel] [RFC PATCH qemu 3/4] memory: Share flat views and dispatch trees between address spaces, Alexey Kardashevskiy, 2017/09/07
[Qemu-devel] [RFC PATCH qemu 2/4] memory: Prepare for shared flat views, Alexey Kardashevskiy, 2017/09/07
Re: [Qemu-devel] [RFC PATCH qemu 0/4] memory: Reduce memory use, Dr. David Alan Gilbert, 2017/09/07