[PATCH 5.17 735/772] bcache: remove incremental dirty sector counting for bch_sectors_dirty_init()

Greg Kroah-Hartman
2022-06-07T22:07:59Z

From: Coly Li <colyli@suse.de>

commit 80db4e4707e78cb22287da7d058d7274bd4cb370 upstream.

After making bch_sectors_dirty_init() being multithreaded, the existing
incremental dirty sector counting in bch_root_node_dirty_init() doesn't
release btree occupation after iterating 500000 (INIT_KEYS_EACH_TIME)
bkeys. Because a read lock is added on btree root node to prevent the
btree to be split during the dirty sectors counting, other I/O requester
has no chance to gain the write lock even restart bcache_btree().

That is to say, the incremental dirty sectors counting is incompatible
to the multhreaded bch_sectors_dirty_init(). We have to choose one and
drop another one.

In my testing, with 512 bytes random writes, I generate 1.2T dirty data
and a btree with 400K nodes. With single thread and incremental dirty
sectors counting, it takes 30+ minites to register the backing device.
And with multithreaded dirty sectors counting, the backing device
registration can be accomplished within 2 minutes.

The 30+ minutes V.S. 2- minutes difference makes me decide to keep
multithreaded bch_sectors_dirty_init() and drop the incremental dirty
sectors counting. This is what this patch does.

But INIT_KEYS_EACH_TIME is kept, in sectors_dirty_init_fn() the CPU
will be released by cond_resched() after every INIT_KEYS_EACH_TIME keys
iterated. This is to avoid the watchdog reports a bogus soft lockup
warning.

Fixes: b144e45fc576 ("bcache: make bch_sectors_dirty_init() to be multithreaded")
Signed-off-by: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220524102336.10684-4-colyli@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/md/bcache/writeback.c | 39 ++++++++++++---------------------------
1 file changed, 12 insertions(+), 27 deletions(-)

--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -802,13 +802,11 @@ static int bch_writeback_thread(void *ar

/* Init */
#define INIT_KEYS_EACH_TIME 500000
-#define INIT_KEYS_SLEEP_MS 100

struct sectors_dirty_init {
struct btree_op op;
unsigned int inode;
size_t count;
- struct bkey start;
};

static int sectors_dirty_init_fn(struct btree_op *_op, struct btree *b,
@@ -824,11 +822,8 @@ static int sectors_dirty_init_fn(struct
KEY_START(k), KEY_SIZE(k));

op->count++;
- if (atomic_read(&b->c->search_inflight) &&
- !(op->count % INIT_KEYS_EACH_TIME)) {
- bkey_copy_key(&op->start, k);
- return -EAGAIN;
- }
+ if (!(op->count % INIT_KEYS_EACH_TIME))
+ cond_resched();

return MAP_CONTINUE;
}
@@ -843,24 +838,16 @@ static int bch_root_node_dirty_init(stru
bch_btree_op_init(&op.op, -1);
op.inode = d->id;
op.count = 0;
- op.start = KEY(op.inode, 0, 0);

- do {
- ret = bcache_btree(map_keys_recurse,
- k,
- c->root,
- &op.op,
- &op.start,
- sectors_dirty_init_fn,
- 0);
- if (ret == -EAGAIN)
- schedule_timeout_interruptible(
- msecs_to_jiffies(INIT_KEYS_SLEEP_MS));
- else if (ret < 0) {
- pr_warn("sectors dirty init failed, ret=%d!\n", ret);
- break;
- }
- } while (ret == -EAGAIN);
+ ret = bcache_btree(map_keys_recurse,
+ k,
+ c->root,
+ &op.op,
+ &KEY(op.inode, 0, 0),
+ sectors_dirty_init_fn,
+ 0);
+ if (ret < 0)
+ pr_warn("sectors dirty init failed, ret=%d!\n", ret);

return ret;
}
@@ -904,7 +891,6 @@ static int bch_dirty_init_thread(void *a
goto out;
}
skip_nr--;
- cond_resched();
}

if (p) {
@@ -914,7 +900,6 @@ static int bch_dirty_init_thread(void *a

p = NULL;
prev_idx = cur_idx;
- cond_resched();
}

out:
@@ -953,11 +938,11 @@ void bch_sectors_dirty_init(struct bcach
bch_btree_op_init(&op.op, -1);
op.inode = d->id;
op.count = 0;
- op.start = KEY(op.inode, 0, 0);

for_each_key_filter(&c->root->keys,
k, &iter, bch_ptr_invalid)
sectors_dirty_init_fn(&op.op, c->root, k);
+
rw_unlock(0, c->root);
return;
}