Thank you Boris for your comments. I removed faulty email of mine.
replies inline.
On 11/30/2018 12:42 PM, Boris Ostrovsky wrote:
On 11/29/18 12:17 AM, Manjunath Patil wrote:
Hi,
Feel free to suggest/comment on this.
I am trying to do the following at dst during the migration now.
1. Dont clear the old rinfo in blkif_free(). Instead just clean it.
2. Store the old rinfo and nr_rings into temp variables in negotiate_mq()
3. let nr_rings get re-calculated based on backend data
4. try allocating new memory based on new nr_rings
Since I suspect number of rings will likely be the same why not reuse
the rings in the common case?
I thought attaching devices will be more often than migration. Hence did
not want add to an extra check for
- if I am inside migration code path and
- if new nr_rings is equal to old nr_rings or not
Sure addition of such a thing would avoid the memory allocation
altogether in migration path,
but it would add a little overhead for normal device addition.
Do you think its worth adding that change?
5.
a. If memory allocation is a success
- free the old rinfo and proceed to use the new rinfo
b. If memory allocation is a failure
- use the old the rinfo
- adjust the nr_rings to the lowest of new nr_rings and old nr_rings
@@ -1918,10 +1936,24 @@ static int negotiate_mq(struct blkfront_info *info)
sizeof(struct blkfront_ring_info),
GFP_KERNEL);
if (!info->rinfo) {
- xenbus_dev_fatal(info->xbdev, -ENOMEM, "allocating ring_info structure");
- info->nr_rings = 0;
- return -ENOMEM;
- }
+ if (unlikely(nr_rings_old)) {
+ /* We might waste some memory if
+ * info->nr_rings < nr_rings_old
+ */
+ info->rinfo = rinfo_old;
+ if (info->nr_rings > nr_rings_old)
+ info->nr_rings = nr_rings_old;
+ xenbus_dev_fatal(info->xbdev, -ENOMEM,
Why xenbus_dev_fatal()?
I wanted to make sure that this msg is seen on console by default. So
that we know there was a enomem event happened and we recovered from it.
What do you suggest instead? xenbus_dev_error?
-boris
+ "reusing old ring_info structure(new ring size=%d)",
+ info->nr_rings);
+ } else {
+ xenbus_dev_fatal(info->xbdev, -ENOMEM,
+ "allocating ring_info structure");
+ info->nr_rings = 0;
+ return -ENOMEM;
+ }
+ } else if (unlikely(nr_rings_old))
+ kfree(rinfo_old);
for (i = 0; i < info->nr_rings; i++) {
struct blkfront_ring_info *rinfo;
