linux-kernel - Re: [PATCH v17 4/6] virtio-balloon: VIRTIO_BALLOON_F

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Date:   Mon, 06 Nov 2017 16:21:06 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-mm@...ck.org, mst@...hat.com,
        mhocko@...nel.org, akpm@...ux-foundation.org,
        mawilcox@...rosoft.com
CC:     david@...hat.com, cornelia.huck@...ibm.com,
        mgorman@...hsingularity.net, aarcange@...hat.com,
        amit.shah@...hat.com, pbonzini@...hat.com, willy@...radead.org,
        liliang.opensource@...il.com, yang.zhang.wz@...il.com,
        quan.xu@...yun.com
Subject: Re: [PATCH v17 4/6] virtio-balloon: VIRTIO_BALLOON_F_SG

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