On Tue, 19 Sep 2017, Ilya Dryomov wrote:
> This reverts most of commit f53b7665c8ce ("libceph: upmap semantic
> changes").
>
> We need to prevent duplicates in the final result. For example, we
> can currently take
>
> [1,2,3] and apply [(1,2)] and get [2,2,3]
>
> or
>
> [1,2,3] and apply [(3,2)] and get [1,2,2]
>
> The rest of the system is not prepared to handle duplicates in the
> result set like this.
>
> The reverted piece was intended to allow
>
> [1,2,3] and [(1,2),(2,1)] to get [2,1,3]
>
> to reorder primaries. First, this bidirectional swap is hard to
> implement in a way that also prevents dups. For example, [1,2,3] and
> [(1,4),(2,3),(3,4)] would give [4,3,4] but would we just drop the last
> step we'd have [4,3,3] which is also invalid, etc. Simpler to just not
> handle bidirectional swaps. In practice, they are not needed: if you
> just want to choose a different primary then use primary_affinity, or
> pg_upmap (not pg_upmap_items).
>
> Cc: stable@xxxxxxxxxxxxxxx # 4.13
> Link: http://tracker.ceph.com/issues/21410
> Signed-off-by: Ilya Dryomov <idryomov@xxxxxxxxx>
Reviewed-by: Sage Weil <sage@xxxxxxxxxx>
Thanks!
sage
> ---
> net/ceph/osdmap.c | 35 +++++++++++++++++++++++++----------
> 1 file changed, 25 insertions(+), 10 deletions(-)
>
> diff --git a/net/ceph/osdmap.c b/net/ceph/osdmap.c
> index f358d0bfa76b..79d14d70b7ea 100644
> --- a/net/ceph/osdmap.c
> +++ b/net/ceph/osdmap.c
> @@ -2445,19 +2445,34 @@ static void apply_upmap(struct ceph_osdmap *osdmap,
>
> pg = lookup_pg_mapping(&osdmap->pg_upmap_items, pgid);
> if (pg) {
> - for (i = 0; i < raw->size; i++) {
> - for (j = 0; j < pg->pg_upmap_items.len; j++) {
> - int from = pg->pg_upmap_items.from_to[j][0];
> - int to = pg->pg_upmap_items.from_to[j][1];
> -
> - if (from == raw->osds[i]) {
> - if (!(to != CRUSH_ITEM_NONE &&
> - to < osdmap->max_osd &&
> - osdmap->osd_weight[to] == 0))
> - raw->osds[i] = to;
> + /*
> + * Note: this approach does not allow a bidirectional swap,
> + * e.g., [[1,2],[2,1]] applied to [0,1,2] -> [0,2,1].
> + */
> + for (i = 0; i < pg->pg_upmap_items.len; i++) {
> + int from = pg->pg_upmap_items.from_to[i][0];
> + int to = pg->pg_upmap_items.from_to[i][1];
> + int pos = -1;
> + bool exists = false;
> +
> + /* make sure replacement doesn't already appear */
> + for (j = 0; j < raw->size; j++) {
> + int osd = raw->osds[j];
> +
> + if (osd == to) {
> + exists = true;
> break;
> }
> + /* ignore mapping if target is marked out */
> + if (osd == from && pos < 0 &&
> + !(to != CRUSH_ITEM_NONE &&
> + to < osdmap->max_osd &&
> + osdmap->osd_weight[to] == 0)) {
> + pos = j;
> + }
> }
> + if (!exists && pos >= 0)
> + raw->osds[pos] = to;
> }
> }
> }
> --
> 2.4.3
>
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