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virtio-balloon: Simplify deflate with pbp 

Let's simplify this - the case we are optimizing for is very hard to
trigger and not worth the effort. If we're switching from inflation to
deflation, let's reset the pbp.

Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20190722134108.22151-4-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
David Hildenbrand 2019-07-22 15:41:05 +02:00 committed by Michael S. Tsirkin
parent 483f13524b
commit 2ffc49eea1
1 changed files with 5 additions and 21 deletions
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26
hw/virtio/virtio-balloon.c
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@ -117,7 +117,7 @@ static void balloon_deflate_page(VirtIOBalloon *balloon,
void *addr = memory_region_get_ram_ptr(mr) + offset;
RAMBlock *rb;
size_t rb_page_size;
ram_addr_t ram_offset, host_page_base;
ram_addr_t ram_offset;
void *host_addr;
int ret;
@ -125,27 +125,11 @@ static void balloon_deflate_page(VirtIOBalloon *balloon,
* host address? */
rb = qemu_ram_block_from_host(addr, false, &ram_offset);
rb_page_size = qemu_ram_pagesize(rb);
host_page_base = ram_offset & ~(rb_page_size - 1);
if (balloon->pbp
&& rb == balloon->pbp->rb
&& host_page_base == balloon->pbp->base) {
int subpages = rb_page_size / BALLOON_PAGE_SIZE;
/*
* This means the guest has asked to discard some of the 4kiB
* subpages of a host page, but then changed its mind and
* asked to keep them after all. It's exceedingly unlikely
* for a guest to do this in practice, but handle it anyway,
* since getting it wrong could mean discarding memory the
* guest is still using. */
clear_bit((ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE,
balloon->pbp->bitmap);
if (bitmap_empty(balloon->pbp->bitmap, subpages)) {
g_free(balloon->pbp);
balloon->pbp = NULL;
}
if (balloon->pbp) {
/* Let's play safe and always reset the pbp on deflation requests. */
g_free(balloon->pbp);
balloon->pbp = NULL;
}
host_addr = (void *)((uintptr_t)addr & ~(rb_page_size - 1));