From: Mathieu Desnoyers Date: Tue, 20 Dec 2011 16:14:01 +0000 (-0500) Subject: Document that flags could be represented on 2 bits X-Git-Tag: v0.7.0~43^2~10 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=13f656f996861f47172f34a1ef28e338616ff5e2;p=userspace-rcu.git Document that flags could be represented on 2 bits Suggested-by: Lai Jiangshan Signed-off-by: Mathieu Desnoyers --- diff --git a/urcu/rculfhash.h b/urcu/rculfhash.h index f337622..de34fae 100644 --- a/urcu/rculfhash.h +++ b/urcu/rculfhash.h @@ -40,7 +40,14 @@ extern "C" { * value required for lookup and traversal of the hash table. * * struct cds_lfht_node should be aligned on 8-bytes boundaries because - * the three lower bits are used as flags. + * the three lower bits are used as flags. It is worth noting that the + * information contained within these three bits could be represented on + * two bits by re-using the same bit for REMOVAL_OWNER_FLAG and + * BUCKET_FLAG. This can be done if we ensure that no iterator nor + * updater check the BUCKET_FLAG after it detects that the REMOVED_FLAG + * is set. Given the minimum size of struct cds_lfht_node is 8 bytes on + * 32-bit architectures, we choose to go for simplicity and reserve + * three bits. * * struct cds_lfht_node can be embedded into a structure (as a field). * caa_container_of() can be used to get the structure from the struct