From: David Hildenbrand <david@redhat.com> To: "Dr. David Alan Gilbert" <dgilbert@redhat.com> Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, qemu-s390x@nongnu.org, Richard Henderson <rth@twiddle.net>, Paolo Bonzini <pbonzini@redhat.com>, Eduardo Habkost <ehabkost@redhat.com>, "Michael S . Tsirkin" <mst@redhat.com> Subject: Re: [PATCH v1 01/17] exec: Introduce ram_block_discard_set_(unreliable|required)() Date: Fri, 15 May 2020 16:40:03 +0200 [thread overview] Message-ID: <da581548-5ff8-eb59-15a1-02cd970788ab@redhat.com> (raw) In-Reply-To: <20200515095413.GB2954@work-vm> On 15.05.20 11:54, Dr. David Alan Gilbert wrote: > * David Hildenbrand (david@redhat.com) wrote: >> We want to replace qemu_balloon_inhibit() by something more generic. >> Especially, we want to make sure that technologies that really rely on >> RAM block discards to work reliably to run mutual exclusive with >> technologies that break it. >> >> E.g., vfio will usually pin all guest memory, turning the virtio-balloon >> basically useless and make the VM consume more memory than reported via >> the balloon. While the balloon is special already (=> no guarantees, same >> behavior possible afer reboots and with huge pages), this will be >> different, especially, with virtio-mem. >> >> Let's implement a way such that we can make both types of technology run >> mutually exclusive. We'll convert existing balloon inhibitors in successive >> patches and add some new ones. Add the check to >> qemu_balloon_is_inhibited() for now. We might want to make >> virtio-balloon an acutal inhibitor in the future - however, that >> requires more thought to not break existing setups. >> >> Cc: "Michael S. Tsirkin" <mst@redhat.com> >> Cc: Richard Henderson <rth@twiddle.net> >> Cc: Paolo Bonzini <pbonzini@redhat.com> >> Signed-off-by: David Hildenbrand <david@redhat.com> >> --- >> balloon.c | 3 ++- >> exec.c | 48 +++++++++++++++++++++++++++++++++++++++++++ >> include/exec/memory.h | 41 ++++++++++++++++++++++++++++++++++++ >> 3 files changed, 91 insertions(+), 1 deletion(-) >> >> diff --git a/balloon.c b/balloon.c >> index f104b42961..c49f57c27b 100644 >> --- a/balloon.c >> +++ b/balloon.c >> @@ -40,7 +40,8 @@ static int balloon_inhibit_count; >> >> bool qemu_balloon_is_inhibited(void) >> { >> - return atomic_read(&balloon_inhibit_count) > 0; >> + return atomic_read(&balloon_inhibit_count) > 0 || >> + ram_block_discard_is_broken(); >> } >> >> void qemu_balloon_inhibit(bool state) >> diff --git a/exec.c b/exec.c >> index 2874bb5088..52a6e40e99 100644 >> --- a/exec.c >> +++ b/exec.c >> @@ -4049,4 +4049,52 @@ void mtree_print_dispatch(AddressSpaceDispatch *d, MemoryRegion *root) >> } >> } >> >> +static int ram_block_discard_broken; > > This could do with a comment; if I'm reading this right then > +ve means broken > -ve means required > I'll add to ram_block_discard_broken: "If positive, discarding RAM is broken. If negative, discarding of RAM is required to work correctly." [...] >> >> +/* >> + * Inhibit technologies that rely on discarding of parts of RAM blocks to work >> + * reliably, e.g., to manage the actual amount of memory consumed by the VM >> + * (then, the memory provided by RAM blocks might be bigger than the desired >> + * memory consumption). This *must* be set if: > > 'technologies that rely on discarding of parts of RAM blocks to work > reliably' is pretty long; I'm not sure of a better way of saying it > though. Maybe simply "Inhibit technologies that rely on discarding of pages in RAM blocks to work"? ? -- Thanks, David / dhildenb
WARNING: multiple messages have this Message-ID (diff)
From: David Hildenbrand <david@redhat.com> To: "Dr. David Alan Gilbert" <dgilbert@redhat.com> Cc: Eduardo Habkost <ehabkost@redhat.com>, kvm@vger.kernel.org, "Michael S . Tsirkin" <mst@redhat.com>, qemu-devel@nongnu.org, qemu-s390x@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>, Richard Henderson <rth@twiddle.net> Subject: Re: [PATCH v1 01/17] exec: Introduce ram_block_discard_set_(unreliable|required)() Date: Fri, 15 May 2020 16:40:03 +0200 [thread overview] Message-ID: <da581548-5ff8-eb59-15a1-02cd970788ab@redhat.com> (raw) In-Reply-To: <20200515095413.GB2954@work-vm> On 15.05.20 11:54, Dr. David Alan Gilbert wrote: > * David Hildenbrand (david@redhat.com) wrote: >> We want to replace qemu_balloon_inhibit() by something more generic. >> Especially, we want to make sure that technologies that really rely on >> RAM block discards to work reliably to run mutual exclusive with >> technologies that break it. >> >> E.g., vfio will usually pin all guest memory, turning the virtio-balloon >> basically useless and make the VM consume more memory than reported via >> the balloon. While the balloon is special already (=> no guarantees, same >> behavior possible afer reboots and with huge pages), this will be >> different, especially, with virtio-mem. >> >> Let's implement a way such that we can make both types of technology run >> mutually exclusive. We'll convert existing balloon inhibitors in successive >> patches and add some new ones. Add the check to >> qemu_balloon_is_inhibited() for now. We might want to make >> virtio-balloon an acutal inhibitor in the future - however, that >> requires more thought to not break existing setups. >> >> Cc: "Michael S. Tsirkin" <mst@redhat.com> >> Cc: Richard Henderson <rth@twiddle.net> >> Cc: Paolo Bonzini <pbonzini@redhat.com> >> Signed-off-by: David Hildenbrand <david@redhat.com> >> --- >> balloon.c | 3 ++- >> exec.c | 48 +++++++++++++++++++++++++++++++++++++++++++ >> include/exec/memory.h | 41 ++++++++++++++++++++++++++++++++++++ >> 3 files changed, 91 insertions(+), 1 deletion(-) >> >> diff --git a/balloon.c b/balloon.c >> index f104b42961..c49f57c27b 100644 >> --- a/balloon.c >> +++ b/balloon.c >> @@ -40,7 +40,8 @@ static int balloon_inhibit_count; >> >> bool qemu_balloon_is_inhibited(void) >> { >> - return atomic_read(&balloon_inhibit_count) > 0; >> + return atomic_read(&balloon_inhibit_count) > 0 || >> + ram_block_discard_is_broken(); >> } >> >> void qemu_balloon_inhibit(bool state) >> diff --git a/exec.c b/exec.c >> index 2874bb5088..52a6e40e99 100644 >> --- a/exec.c >> +++ b/exec.c >> @@ -4049,4 +4049,52 @@ void mtree_print_dispatch(AddressSpaceDispatch *d, MemoryRegion *root) >> } >> } >> >> +static int ram_block_discard_broken; > > This could do with a comment; if I'm reading this right then > +ve means broken > -ve means required > I'll add to ram_block_discard_broken: "If positive, discarding RAM is broken. If negative, discarding of RAM is required to work correctly." [...] >> >> +/* >> + * Inhibit technologies that rely on discarding of parts of RAM blocks to work >> + * reliably, e.g., to manage the actual amount of memory consumed by the VM >> + * (then, the memory provided by RAM blocks might be bigger than the desired >> + * memory consumption). This *must* be set if: > > 'technologies that rely on discarding of parts of RAM blocks to work > reliably' is pretty long; I'm not sure of a better way of saying it > though. Maybe simply "Inhibit technologies that rely on discarding of pages in RAM blocks to work"? ? -- Thanks, David / dhildenb
next prev parent reply other threads:[~2020-05-15 14:40 UTC|newest] Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-05-06 9:49 [PATCH v1 00/17] virtio-mem: Paravirtualized memory hot(un)plug David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-06 9:49 ` [PATCH v1 01/17] exec: Introduce ram_block_discard_set_(unreliable|required)() David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-15 9:54 ` Dr. David Alan Gilbert 2020-05-15 9:54 ` Dr. David Alan Gilbert 2020-05-15 14:40 ` David Hildenbrand [this message] 2020-05-15 14:40 ` David Hildenbrand 2020-05-15 14:54 ` David Hildenbrand 2020-05-15 14:54 ` David Hildenbrand 2020-05-15 16:15 ` Dr. David Alan Gilbert 2020-05-15 16:15 ` Dr. David Alan Gilbert 2020-05-06 9:49 ` [PATCH v1 02/17] vfio: Convert to ram_block_discard_set_broken() David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-15 12:01 ` David Hildenbrand 2020-05-15 12:01 ` David Hildenbrand 2020-05-06 9:49 ` [PATCH v1 03/17] accel/kvm: " David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-15 11:57 ` Dr. David Alan Gilbert 2020-05-15 11:57 ` Dr. David Alan Gilbert 2020-05-06 9:49 ` [PATCH v1 04/17] s390x/pv: " David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-06 9:49 ` [PATCH v1 05/17] virtio-balloon: Rip out qemu_balloon_inhibit() David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-15 12:09 ` Dr. David Alan Gilbert 2020-05-15 12:09 ` Dr. David Alan Gilbert 2020-05-15 12:12 ` David Hildenbrand 2020-05-15 12:12 ` David Hildenbrand 2020-05-06 9:49 ` [PATCH v1 06/17] target/i386: sev: Use ram_block_discard_set_broken() David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-15 15:51 ` Dr. David Alan Gilbert 2020-05-15 15:51 ` Dr. David Alan Gilbert 2020-05-06 9:49 ` [PATCH v1 07/17] migration/rdma: " David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-15 12:45 ` Dr. David Alan Gilbert 2020-05-15 12:45 ` Dr. David Alan Gilbert 2020-05-15 14:09 ` David Hildenbrand 2020-05-15 14:09 ` David Hildenbrand 2020-05-15 17:51 ` Dr. David Alan Gilbert 2020-05-15 17:51 ` Dr. David Alan Gilbert 2020-05-15 17:59 ` David Hildenbrand 2020-05-15 17:59 ` David Hildenbrand 2020-05-15 18:36 ` Dr. David Alan Gilbert 2020-05-15 18:36 ` Dr. David Alan Gilbert 2020-05-18 13:52 ` David Hildenbrand 2020-05-18 13:52 ` David Hildenbrand 2020-05-06 9:49 ` [PATCH v1 08/17] migration/colo: " David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-15 13:58 ` Dr. David Alan Gilbert 2020-05-15 13:58 ` Dr. David Alan Gilbert 2020-05-15 14:05 ` David Hildenbrand 2020-05-15 14:05 ` David Hildenbrand 2020-05-06 9:49 ` [PATCH v1 09/17] linux-headers: update to contain virtio-mem David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-06 9:49 ` [PATCH v1 10/17] virtio-mem: Paravirtualized memory hot(un)plug David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-06 16:12 ` Eric Blake 2020-05-06 16:12 ` Eric Blake 2020-05-06 16:14 ` David Hildenbrand 2020-05-06 16:14 ` David Hildenbrand 2020-05-15 15:37 ` Dr. David Alan Gilbert 2020-05-15 15:37 ` Dr. David Alan Gilbert 2020-05-15 16:48 ` David Hildenbrand 2020-05-15 16:48 ` David Hildenbrand 2020-05-18 14:23 ` David Hildenbrand 2020-05-18 14:23 ` David Hildenbrand 2020-05-06 9:49 ` [PATCH v1 11/17] virtio-pci: Proxy for virtio-mem David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-06 18:57 ` Pankaj Gupta 2020-05-06 18:57 ` Pankaj Gupta 2020-05-18 13:34 ` David Hildenbrand 2020-05-18 13:34 ` David Hildenbrand 2020-05-06 9:49 ` [PATCH v1 12/17] MAINTAINERS: Add myself as virtio-mem maintainer David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-15 15:55 ` Dr. David Alan Gilbert 2020-05-15 15:55 ` Dr. David Alan Gilbert 2020-05-06 9:49 ` [PATCH v1 13/17] hmp: Handle virtio-mem when printing memory device info David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-06 19:03 ` Pankaj Gupta 2020-05-06 19:03 ` Pankaj Gupta 2020-05-06 9:49 ` [PATCH v1 14/17] numa: Handle virtio-mem in NUMA stats David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-06 9:49 ` [PATCH v1 15/17] pc: Support for virtio-mem-pci David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-06 12:19 ` Pankaj Gupta 2020-05-06 12:19 ` Pankaj Gupta 2020-05-06 9:49 ` [PATCH v1 16/17] virtio-mem: Allow notifiers for size changes David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-15 16:46 ` Dr. David Alan Gilbert 2020-05-15 16:46 ` Dr. David Alan Gilbert 2020-05-06 9:49 ` [PATCH v1 17/17] virtio-pci: Send qapi events when the virtio-mem " David Hildenbrand 2020-05-06 9:49 ` David Hildenbrand 2020-05-15 15:18 ` David Hildenbrand 2020-05-15 15:18 ` David Hildenbrand
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