diff options
Diffstat (limited to 'include/sys/metaslab_impl.h')
| -rw-r--r-- | include/sys/metaslab_impl.h | 32 |
1 files changed, 25 insertions, 7 deletions
diff --git a/include/sys/metaslab_impl.h b/include/sys/metaslab_impl.h index 386f6240c..a36baedd4 100644 --- a/include/sys/metaslab_impl.h +++ b/include/sys/metaslab_impl.h @@ -67,20 +67,38 @@ struct metaslab_group { }; /* - * Each metaslab's free space is tracked in space map object in the MOS, - * which is only updated in syncing context. Each time we sync a txg, + * Each metaslab maintains an in-core free map (ms_map) that contains the + * current list of free segments. As blocks are allocated, the allocated + * segment is removed from the ms_map and added to a per txg allocation map. + * As blocks are freed, they are added to the per txg free map. These per + * txg maps allow us to process all allocations and frees in syncing context + * where it is safe to update the on-disk space maps. + * + * Each metaslab's free space is tracked in a space map object in the MOS, + * which is only updated in syncing context. Each time we sync a txg, * we append the allocs and frees from that txg to the space map object. * When the txg is done syncing, metaslab_sync_done() updates ms_smo - * to ms_smo_syncing. Everything in ms_smo is always safe to allocate. + * to ms_smo_syncing. Everything in ms_smo is always safe to allocate. + * + * To load the in-core free map we read the space map object from disk. + * This object contains a series of alloc and free records that are + * combined to make up the list of all free segments in this metaslab. These + * segments are represented in-core by the ms_map and are stored in an + * AVL tree. + * + * As the space map objects grows (as a result of the appends) it will + * eventually become space-inefficient. When the space map object is + * zfs_condense_pct/100 times the size of the minimal on-disk representation, + * we rewrite it in its minimized form. */ struct metaslab { kmutex_t ms_lock; /* metaslab lock */ space_map_obj_t ms_smo; /* synced space map object */ space_map_obj_t ms_smo_syncing; /* syncing space map object */ - space_map_t ms_allocmap[TXG_SIZE]; /* allocated this txg */ - space_map_t ms_freemap[TXG_SIZE]; /* freed this txg */ - space_map_t ms_defermap[TXG_DEFER_SIZE]; /* deferred frees */ - space_map_t ms_map; /* in-core free space map */ + space_map_t *ms_allocmap[TXG_SIZE]; /* allocated this txg */ + space_map_t *ms_freemap[TXG_SIZE]; /* freed this txg */ + space_map_t *ms_defermap[TXG_DEFER_SIZE]; /* deferred frees */ + space_map_t *ms_map; /* in-core free space map */ int64_t ms_deferspace; /* sum of ms_defermap[] space */ uint64_t ms_weight; /* weight vs. others in group */ metaslab_group_t *ms_group; /* metaslab group */ |