diff options
| -rw-r--r-- | fs/ubifs/gc.c | 20 | ||||
| -rw-r--r-- | fs/ubifs/super.c | 11 | ||||
| -rw-r--r-- | fs/ubifs/ubifs.h | 4 |
3 files changed, 24 insertions, 11 deletions
diff --git a/fs/ubifs/gc.c b/fs/ubifs/gc.c index 9832f9a..b2e5f11 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> diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c index 53811e5..da99da0 100644 --- a/fs/ubifs/super.c +++ b/fs/ubifs/super.c @@ -573,15 +573,8 @@ static int init_constants_early(struct ubifs_info *c) c->ranges[UBIFS_IDX_NODE].max_len = INT_MAX; /* - * Initialize dead and dark LEB space watermarks. - * - * Dead space is the space which cannot be used. Its watermark is - * equivalent to min. I/O unit or minimum node size if it is greater - * then min. I/O unit. - * - * Dark space is the space which might be used, or might not, depending - * on which node should be written to the LEB. Its watermark is - * equivalent to maximum UBIFS node size. + * Initialize dead and dark LEB space watermarks. See gc.c for comments + * about these values. */ c->dead_wm = ALIGN(MIN_WRITE_SZ, c->min_io_size); c->dark_wm = ALIGN(UBIFS_MAX_NODE_SZ, c->min_io_size); diff --git a/fs/ubifs/ubifs.h b/fs/ubifs/ubifs.h index 0881897..2e78d6a 100644 --- a/fs/ubifs/ubifs.h +++ b/fs/ubifs/ubifs.h @@ -426,9 +426,9 @@ struct ubifs_unclean_leb { * LEB properties flags. * * LPROPS_UNCAT: not categorized - * LPROPS_DIRTY: dirty > 0, not index + * LPROPS_DIRTY: dirty > free, dirty >= @c->dead_wm, not index * LPROPS_DIRTY_IDX: dirty + free > @c->min_idx_node_sze and index - * LPROPS_FREE: free > 0, not empty, not index + * LPROPS_FREE: free > 0, dirty < @c->dead_wm, not empty, not index * LPROPS_HEAP_CNT: number of heaps used for storing categorized LEBs * LPROPS_EMPTY: LEB is empty, not taken * LPROPS_FREEABLE: free + dirty == leb_size, not index, not taken |
