diff options
| -rw-r--r-- | drivers/md/bcache/writeback.c | 31 | ||||
| -rw-r--r-- | drivers/md/bcache/writeback.h | 7 |
2 files changed, 34 insertions, 4 deletions
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 31b0a292a619..51306a19ab03 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -18,17 +18,39 @@ #include <trace/events/bcache.h> /* Rate limiting */ - -static void __update_writeback_rate(struct cached_dev *dc) +static uint64_t __calc_target_rate(struct cached_dev *dc) { struct cache_set *c = dc->disk.c; + + /* + * This is the size of the cache, minus the amount used for + * flash-only devices + */ uint64_t cache_sectors = c->nbuckets * c->sb.bucket_size - bcache_flash_devs_sectors_dirty(c); + + /* + * Unfortunately there is no control of global dirty data. If the + * user states that they want 10% dirty data in the cache, and has, + * e.g., 5 backing volumes of equal size, we try and ensure each + * backing volume uses about 2% of the cache for dirty data. + */ + uint32_t bdev_share = + div64_u64(bdev_sectors(dc->bdev) << WRITEBACK_SHARE_SHIFT, + c->cached_dev_sectors); + uint64_t cache_dirty_target = div_u64(cache_sectors * dc->writeback_percent, 100); - int64_t target = div64_u64(cache_dirty_target * bdev_sectors(dc->bdev), - c->cached_dev_sectors); + /* Ensure each backing dev gets at least one dirty share */ + if (bdev_share < 1) + bdev_share = 1; + + return (cache_dirty_target * bdev_share) >> WRITEBACK_SHARE_SHIFT; +} + +static void __update_writeback_rate(struct cached_dev *dc) +{ /* * PI controller: * Figures out the amount that should be written per second. @@ -49,6 +71,7 @@ static void __update_writeback_rate(struct cached_dev *dc) * This acts as a slow, long-term average that is not subject to * variations in usage like the p term. */ + int64_t target = __calc_target_rate(dc); int64_t dirty = bcache_dev_sectors_dirty(&dc->disk); int64_t error = dirty - target; int64_t proportional_scaled = diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h index f102b1f9bc51..66f1c527fa24 100644 --- a/drivers/md/bcache/writeback.h +++ b/drivers/md/bcache/writeback.h @@ -8,6 +8,13 @@ #define MAX_WRITEBACKS_IN_PASS 5 #define MAX_WRITESIZE_IN_PASS 5000 /* *512b */ +/* + * 14 (16384ths) is chosen here as something that each backing device + * should be a reasonable fraction of the share, and not to blow up + * until individual backing devices are a petabyte. + */ +#define WRITEBACK_SHARE_SHIFT 14 + static inline uint64_t bcache_dev_sectors_dirty(struct bcache_device *d) { uint64_t i, ret = 0; |