From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: "Michael S. Tsirkin" <mst@redhat.com>, Wei Wang <wei.w.wang@intel.com>
Cc: virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
linux-mm@kvack.org, mhocko@kernel.org, akpm@linux-foundation.org,
pbonzini@redhat.com, liliang.opensource@gmail.com,
yang.zhang.wz@gmail.com, quan.xu0@gmail.com, nilal@redhat.com,
riel@redhat.com
Subject: Re: [PATCH v22 2/3] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ
Date: Thu, 18 Jan 2018 22:30:18 +0900 [thread overview]
Message-ID: <2bb0e3d9-1679-9ad3-b402-f0781f6cf094@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20180117180337-mutt-send-email-mst@kernel.org>
On 2018/01/18 1:44, Michael S. Tsirkin wrote:
>> +static void add_one_sg(struct virtqueue *vq, unsigned long pfn, uint32_t len)
>> +{
>> + struct scatterlist sg;
>> + unsigned int unused;
>> + int err;
>> +
>> + sg_init_table(&sg, 1);
>> + sg_set_page(&sg, pfn_to_page(pfn), len, 0);
>> +
>> + /* Detach all the used buffers from the vq */
>> + while (virtqueue_get_buf(vq, &unused))
>> + ;
>> +
>> + /*
>> + * Since this is an optimization feature, losing a couple of free
>> + * pages to report isn't important.
>> We simply resturn
>
> return
>
>> without adding
>> + * the page if the vq is full. We are adding one entry each time,
>> + * which essentially results in no memory allocation, so the
>> + * GFP_KERNEL flag below can be ignored.
>> + */
>> + if (vq->num_free) {
>> + err = virtqueue_add_inbuf(vq, &sg, 1, vq, GFP_KERNEL);
>
> Should we kick here? At least when ring is close to
> being full. Kick at half way full?
> Otherwise it's unlikely ring will
> ever be cleaned until we finish the scan.
Since this add_one_sg() is called between spin_lock_irqsave(&zone->lock, flags)
and spin_unlock_irqrestore(&zone->lock, flags), it is not permitted to sleep.
And walk_free_mem_block() is not ready to handle resume.
By the way, specifying GFP_KERNEL here is confusing even though it is never used.
walk_free_mem_block() says:
* The callback itself must not sleep or perform any operations which would
* require any memory allocations directly (not even GFP_NOWAIT/GFP_ATOMIC)
* or via any lock dependency.
>
>> + /*
>> + * This is expected to never fail, because there is always an
>> + * entry available on the vq.
>> + */
>> + BUG_ON(err);
>> + }
>> +}
next prev parent reply other threads:[~2018-01-18 13:32 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-17 5:10 [PATCH v22 0/3] Virtio-balloon: support free page reporting Wei Wang
2018-01-17 5:10 ` [PATCH v22 1/3] mm: support reporting free page blocks Wei Wang
2018-01-17 5:10 ` [PATCH v22 2/3] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ Wei Wang
2018-01-17 8:21 ` Pankaj Gupta
2018-01-17 9:00 ` Wei Wang
2018-01-17 9:27 ` Pankaj Gupta
2018-01-17 10:47 ` Wei Wang
2018-01-17 16:44 ` Michael S. Tsirkin
2018-01-18 13:30 ` Tetsuo Handa [this message]
2018-01-18 19:09 ` Michael S. Tsirkin
2018-01-18 21:11 ` Tetsuo Handa
2018-01-18 22:32 ` Michael S. Tsirkin
2018-01-20 14:23 ` Tetsuo Handa
2018-01-19 3:44 ` Wei Wang
2018-01-19 12:39 ` Michael S. Tsirkin
2018-01-22 11:25 ` [virtio-dev] " Wei Wang
2018-01-24 3:18 ` Wei Wang
2018-01-24 4:31 ` Michael S. Tsirkin
2018-01-24 4:29 ` Michael S. Tsirkin
2018-01-24 11:28 ` Wei Wang
2018-01-19 6:24 ` Wei Wang
2018-01-17 5:10 ` [PATCH v22 3/3] virtio-balloon: don't report free pages when page poisoning is enabled Wei Wang
2018-01-18 22:37 ` Michael S. Tsirkin
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