| Message ID | 20190306030601.21986-4-david@gibson.dropbear.id.au (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | virtio-balloon: Several fixes to recent rework | expand |
On 06.03.19 04:06, David Gibson wrote: > Prior to f6deb6d9 "virtio-balloon: Remove unnecessary MADV_WILLNEED on > deflate", the balloon device issued an madvise() MADV_WILLNEED on > pages removed from the balloon. That would hint to the host kernel > that the pages were likely to be needed by the guest in the near > future. > > It's unclear if this is actually valuable or not, and so f6deb6d9 > removed this, essentially ignoring balloon deflate requests. However, > concerns have been raised that this might cause a performance > regression by causing extra latency for the guest in certain > configurations. > > So, until we can get actual benchmark data to see if that's the case, > this restores the old behaviour, issuing a MADV_WILLNEED when a page is > removed from the balloon. > > Signed-off-by: David Gibson <david@gibson.dropbear.id.au> > --- > hw/virtio/virtio-balloon.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c > index 7412bf8c85..ac36988605 100644 > --- a/hw/virtio/virtio-balloon.c > +++ b/hw/virtio/virtio-balloon.c > @@ -118,6 +118,8 @@ static void balloon_deflate_page(VirtIOBalloon *balloon, > RAMBlock *rb; > size_t rb_page_size; > ram_addr_t ram_offset, host_page_base; > + void *host_addr; > + int ret; > > /* XXX is there a better way to get to the RAMBlock than via a > * host address? */ > @@ -146,6 +148,17 @@ static void balloon_deflate_page(VirtIOBalloon *balloon, > balloon->pbp = NULL; > } > } > + > + host_addr = (void *)((uintptr_t)addr & ~(rb_page_size - 1)); > + > + /* When a page is deflated, we hint the whole host page it lives > + * on, since we can't do anything smaller */ > + ret = qemu_madvise(host_addr, rb_page_size, QEMU_MADV_WILLNEED); > + if (ret != 0) { > + warn_report("Couldn't MADV_WILLNEED on balloon deflate: %s", > + strerror(errno)); > + /* Otherwise ignore, failing to page hint shouldn't be fatal */ > + } As far as I understand the man page, only MADV_DONTNEED will complain about locked, huge or VM_PFNMAP pages. So I guess MADV_WILLNEED will work for these cases (in the worst case be a NOP).
diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c index 7412bf8c85..ac36988605 100644 --- a/hw/virtio/virtio-balloon.c +++ b/hw/virtio/virtio-balloon.c @@ -118,6 +118,8 @@ static void balloon_deflate_page(VirtIOBalloon *balloon, RAMBlock *rb; size_t rb_page_size; ram_addr_t ram_offset, host_page_base; + void *host_addr; + int ret; /* XXX is there a better way to get to the RAMBlock than via a * host address? */ @@ -146,6 +148,17 @@ static void balloon_deflate_page(VirtIOBalloon *balloon, balloon->pbp = NULL; } } + + host_addr = (void *)((uintptr_t)addr & ~(rb_page_size - 1)); + + /* When a page is deflated, we hint the whole host page it lives + * on, since we can't do anything smaller */ + ret = qemu_madvise(host_addr, rb_page_size, QEMU_MADV_WILLNEED); + if (ret != 0) { + warn_report("Couldn't MADV_WILLNEED on balloon deflate: %s", + strerror(errno)); + /* Otherwise ignore, failing to page hint shouldn't be fatal */ + } } static const char *balloon_stat_names[] = {
Prior to f6deb6d9 "virtio-balloon: Remove unnecessary MADV_WILLNEED on deflate", the balloon device issued an madvise() MADV_WILLNEED on pages removed from the balloon. That would hint to the host kernel that the pages were likely to be needed by the guest in the near future. It's unclear if this is actually valuable or not, and so f6deb6d9 removed this, essentially ignoring balloon deflate requests. However, concerns have been raised that this might cause a performance regression by causing extra latency for the guest in certain configurations. So, until we can get actual benchmark data to see if that's the case, this restores the old behaviour, issuing a MADV_WILLNEED when a page is removed from the balloon. Signed-off-by: David Gibson <david@gibson.dropbear.id.au> --- hw/virtio/virtio-balloon.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)