From 596546fe9e4d1d1fa6423c300e2a73b6f90baeb0 Mon Sep 17 00:00:00 2001 From: David Gibson Date: Wed, 6 Mar 2019 14:06:01 +1100 Subject: [PATCH] virtio-balloon: Restore MADV_WILLNEED hint on balloon deflate 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 Message-Id: <20190306030601.21986-4-david@gibson.dropbear.id.au> Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin --- 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 77532e80d5..2112874055 100644 --- a/hw/virtio/virtio-balloon.c +++ b/hw/virtio/virtio-balloon.c @@ -119,6 +119,8 @@ 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? */ @@ -147,6 +149,17 @@ 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[] = { -- 2.11.4.GIT