diff options
Diffstat (limited to 'fs/ubifs/gc.c')
| -rw-r--r-- | fs/ubifs/gc.c | 28 |
1 files changed, 24 insertions, 4 deletions
diff --git a/fs/ubifs/gc.c b/fs/ubifs/gc.c index 9832f9abe28..a711d33b3d3 100644 --- a/fs/ubifs/gc.c +++ b/fs/ubifs/gc.c @@ -31,6 +31,26 @@ * to be reused. Garbage collection will cause the number of dirty index nodes * to grow, however sufficient space is reserved for the index to ensure the * commit will never run out of space. + * + * Notes about dead watermark. At current UBIFS implementation we assume that + * LEBs which have less than @c->dead_wm bytes of free + dirty space are full + * and not worth garbage-collecting. The dead watermark is one min. I/O unit + * size, or min. UBIFS node size, depending on what is greater. Indeed, UBIFS + * Garbage Collector has to synchronize the GC head's write buffer before + * returning, so this is about wasting one min. I/O unit. However, UBIFS GC can + * actually reclaim even very small pieces of dirty space by garbage collecting + * enough dirty LEBs, but we do not bother doing this at this implementation. + * + * Notes about dark watermark. The results of GC work depends on how big are + * the UBIFS nodes GC deals with. Large nodes make GC waste more space. Indeed, + * if GC move data from LEB A to LEB B and nodes in LEB A are large, GC would + * have to waste large pieces of free space at the end of LEB B, because nodes + * from LEB A would not fit. And the worst situation is when all nodes are of + * maximum size. So dark watermark is the amount of free + dirty space in LEB + * which are guaranteed to be reclaimable. If LEB has less space, the GC migh + * be unable to reclaim it. So, LEBs with free + dirty greater than dark + * watermark are "good" LEBs from GC's point of few. The other LEBs are not so + * good, and GC takes extra care when moving them. */ #include <linux/pagemap.h> @@ -381,7 +401,7 @@ int ubifs_garbage_collect_leb(struct ubifs_info *c, struct ubifs_lprops *lp) /* * Don't release the LEB until after the next commit, because - * it may contain date which is needed for recovery. So + * it may contain data which is needed for recovery. So * although we freed this LEB, it will become usable only after * the commit. */ @@ -810,8 +830,9 @@ out: * ubifs_destroy_idx_gc - destroy idx_gc list. * @c: UBIFS file-system description object * - * This function destroys the idx_gc list. It is called when unmounting or - * remounting read-only so locks are not needed. + * This function destroys the @c->idx_gc list. It is called when unmounting + * so locks are not needed. Returns zero in case of success and a negative + * error code in case of failure. */ void ubifs_destroy_idx_gc(struct ubifs_info *c) { @@ -824,7 +845,6 @@ void ubifs_destroy_idx_gc(struct ubifs_info *c) list_del(&idx_gc->list); kfree(idx_gc); } - } /** |