Commit 2ffc49ee authored by David Hildenbrand's avatar David Hildenbrand Committed by Michael S. Tsirkin
Browse files

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: default avatarDavid Gibson <david@gibson.dropbear.id.au>
Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Message-Id: <20190722134108.22151-4-david@redhat.com>
Reviewed-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 483f1352

hw/virtio/virtio-balloon.c

+5 −21
Original line number Diff line number Diff line
@@ -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;
@@ -125,28 +125,12 @@ 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)) {

    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));