Re: [Qemu-devel] [PATCH v17 4/6] virtio-balloon: VIRTIO_BALLOON_F_SG

[Wei Wang]

On 11/04/2017 07:28 PM, Tetsuo Handa wrote:
> Wei Wang wrote:
> > On 11/03/2017 07:25 PM, Tetsuo Handa wrote:
> >
> > If this is inside vb->balloon_lock mutex (isn't this?), xb_set_page() must not
> > use __GFP_DIRECT_RECLAIM allocation, for leak_balloon_sg_oom() will be blocked
> > on vb->balloon_lock mutex.
> > OK. Since the preload() doesn't need too much memory (< 4K in total),
> > how about GFP_NOWAIT here?
> Maybe GFP_NOWAIT | __GFP_NOWARN ?

Sounds good to me. I also plan to move "xb_set_page()" under mutex_lock, 
that is,

    fill_balloon()
    {
        ...
        mutex_lock(&vb->balloon_lock);

        vb->num_pfns = 0;
        while ((page = balloon_page_pop(&pages))) {
==>        xb_set_page(..,page,..);
                balloon_page_enqueue(&vb->vb_dev_info, page);
        ...
    }

As explained in the xbitmap patch, we need the lock to avoid concurrent 
access to the bitmap.

Best,
Wei