linux-kernel - Re: [PATCH v1 02/29] virtio-mem: simplify calculation in virtio_mem_mb_state_prepare_next

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Message-ID: <20201015040204.GB86495@L-31X9LVDL-1304.local>
Date:   Thu, 15 Oct 2020 12:02:04 +0800
From:   Wei Yang <richard.weiyang@...ux.alibaba.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        virtualization@...ts.linux-foundation.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Pankaj Gupta <pankaj.gupta.linux@...il.com>
Subject: Re: [PATCH v1 02/29] virtio-mem: simplify calculation in
 virtio_mem_mb_state_prepare_next_mb()

On Mon, Oct 12, 2020 at 02:52:56PM +0200, David Hildenbrand wrote:
>We actually need one byte less (next_mb_id is exclusive, first_mb_id is
>inclusive). Simplify.
>
>Cc: "Michael S. Tsirkin" <mst@...hat.com>
>Cc: Jason Wang <jasowang@...hat.com>
>Cc: Pankaj Gupta <pankaj.gupta.linux@...il.com>
>Signed-off-by: David Hildenbrand <david@...hat.com>
>---
> drivers/virtio/virtio_mem.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
>index a1f5bf7a571a..670b3faf412d 100644
>--- a/drivers/virtio/virtio_mem.c
>+++ b/drivers/virtio/virtio_mem.c
>@@ -257,8 +257,8 @@ static enum virtio_mem_mb_state virtio_mem_mb_get_state(struct virtio_mem *vm,
>  */
> static int virtio_mem_mb_state_prepare_next_mb(struct virtio_mem *vm)
> {
>-	unsigned long old_bytes = vm->next_mb_id - vm->first_mb_id + 1;
>-	unsigned long new_bytes = vm->next_mb_id - vm->first_mb_id + 2;
>+	unsigned long old_bytes = vm->next_mb_id - vm->first_mb_id;
>+	unsigned long new_bytes = old_bytes + 1;

This is correct.

So this looks more like a fix?

> 	int old_pages = PFN_UP(old_bytes);
> 	int new_pages = PFN_UP(new_bytes);
> 	uint8_t *new_mb_state;
>-- 
>2.26.2

-- 
Wei Yang
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