crush: apply chooseleaf_tries to firstn mode too
Parameterize the attempts for the _firstn choose method, and apply the
rule-specified tries count to firstn mode as well. Note that we have
slightly different behavior here than with indep:
If the firstn value is not specified for firstn, we pass through the
normal attempt count. This maintains compatibility with legacy behavior.
Note that this is usually *not* actually N^2 work, though, because of the
descend_once tunable. However, descend_once is unfortunately *not* the
same thing as 1 chooseleaf try because it is only checked on a reject but
not on a collision. Sigh.
In contrast, for indep, if tries is not specified we default to 1
recursive attempt, because that is simply more sane, and we have the
option to do so. The descend_once tunable has no effect for indep.
Reflects ceph.git commit 64aeded50d80942d66a5ec7b604ff2fcbf5d7b63.
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
diff --git a/include/linux/crush/crush.h b/include/linux/crush/crush.h
index 2e50bab..07b8fd4 100644
--- a/include/linux/crush/crush.h
+++ b/include/linux/crush/crush.h
@@ -165,7 +165,10 @@
__u32 choose_local_fallback_tries;
/* choose attempts before giving up */
__u32 choose_total_tries;
- /* attempt chooseleaf inner descent once; on failure retry outer descent */
+ /* attempt chooseleaf inner descent once for firstn mode; on
+ * reject retry outer descent. Note that this does *not*
+ * apply to a collision: in that case we will retry as we used
+ * to. */
__u32 chooseleaf_descend_once;
};