@@ -369,10 +369,24 @@ static bool check_should_bypass(struct cached_dev *dc, struct bio *bio)
struct io *i;
if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) ||
- c->gc_stats.in_use > CUTOFF_CACHE_ADD ||
(bio_op(bio) == REQ_OP_DISCARD))
goto skip;
+ if (c->gc_stats.in_use > CUTOFF_CACHE_ADD) {
+ /*
+ * If cached buckets are all clean now, 'true' will be
+ * returned and all requests will bypass the cache device.
+ * Then c->sectors_to_gc has no chance to be negative, and
+ * gc thread won't wake up and caching won't work forever.
+ * Here call force_wake_up_gc() to avoid such aftermath.
+ */
+ if (BDEV_STATE(&dc->sb) == BDEV_STATE_CLEAN &&
+ c->gc_mark_valid)
+ force_wake_up_gc(c);
+
+ goto skip;
+ }
+
if (mode == CACHE_MODE_NONE ||
(mode == CACHE_MODE_WRITEAROUND &&
op_is_write(bio_op(bio))))
If there are extreme heavy write I/O continuously hit on relative small cache device (512GB in my testing), it is possible to make counter c->gc_stats.in_use continue to increase and exceed CUTOFF_CACHE_ADD. If 'c->gc_stats.in_use > CUTOFF_CACHE_ADD' happens, all following write requests will bypass the cache device because check_should_bypass() returns 'true'. Because all writes bypass the cache device, counter c->sectors_to_gc has no chance to be negative value, and garbage collection thread won't be waken up even the whole cache becomes clean after writeback accomplished. The aftermath is that all write I/Os go directly into backing device even the cache device is clean. To avoid the above situation, this patch uses a quite conservative way to fix: if 'c->gc_stats.in_use > CUTOFF_CACHE_ADD' happens, only wakes up garbage collection thread when the whole cache device is clean. Before the fix, the writes-always-bypass situation happens after 10+ hours write I/O pressure on 512GB Intel optane memory which acts as cache device. After this fix, such situation doesn't happen after 36+ hours testing. Signed-off-by: Coly Li <colyli@suse.de> --- drivers/md/bcache/request.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-)