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Subject: Re: [RFC] virtio-mem: virtio_mem_init: Access bb_size just in BBM
 mode
To:     Hui Zhu <teawater@gmail.com>, mst@redhat.com, jasowang@redhat.com,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
Cc:     Hui Zhu <teawaterz@linux.alibaba.com>
References: <20210615065948.23493-1-teawater@gmail.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <7fd8bf39-642d-1cdf-bc5d-c19630045013@redhat.com>
Date:   Tue, 15 Jun 2021 09:43:33 +0200
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On 15.06.21 08:59, Hui Zhu wrote:
> From: Hui Zhu <teawaterz@linux.alibaba.com>
> 
> /* In BBM, we also want at least two big blocks. */
> vm->offline_threshold = max_t(uint64_t, 2 * vm->bbm.bb_size,
> 			      vm->offline_threshold);
> This line does not modify vm->offline_threshold depending on the data in
> vm->sbm that shares this address is 0 in SBM mode.
> I think it might be difficult to make sure when we change this in the
> future.
> 
> This commit adds an if to make sure that this line just be executed in
> BBM mode.
> 
> Signed-off-by: Hui Zhu <teawaterz@linux.alibaba.com>
> ---
>   drivers/virtio/virtio_mem.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
> index 10ec60d..8185916 100644
> --- a/drivers/virtio/virtio_mem.c
> +++ b/drivers/virtio/virtio_mem.c
> @@ -2472,8 +2472,9 @@ static int virtio_mem_init(struct virtio_mem *vm)
>   	vm->offline_threshold = max_t(uint64_t, 2 * memory_block_size_bytes(),
>   				      VIRTIO_MEM_DEFAULT_OFFLINE_THRESHOLD);
>   	/* In BBM, we also want at least two big blocks. */
> -	vm->offline_threshold = max_t(uint64_t, 2 * vm->bbm.bb_size,
> -				      vm->offline_threshold);
> +	if (!vm->in_sbm)
> +		vm->offline_threshold = max_t(uint64_t, 2 * vm->bbm.bb_size,
> +					      vm->offline_threshold);
>   
>   	dev_info(&vm->vdev->dev, "start address: 0x%llx", vm->addr);
>   	dev_info(&vm->vdev->dev, "region size: 0x%llx", vm->region_size);
> 

Good that you also spotted it, I already have a fix pending for that :)

https://lkml.kernel.org/r/20210602185720.31821-2-david@redhat.com

-- 
Thanks,

David / dhildenb