Re: [PATCH] bcache: try to reuse the slot of invalid_uuid

[Zou Mingzhe <mingzhe.zou@easystack.cn>]

在 2022/6/6 16:57, Coly Li 写道:
>
>> 2022年6月6日 16:45，mingzhe.zou@easystack.cn 写道：
>>
>> From: mingzhe <mingzhe.zou@easystack.cn>
>>
>>
> [snipped]
>
>> We want to use those invalid_uuid slots carefully. Because, the bkey of the inode
>> may still exist in the btree. So, we need to check the btree before reuse it.
>>
>> Signed-off-by: mingzhe <mingzhe.zou@easystack.cn>
>> ---
>> drivers/md/bcache/btree.c | 35 +++++++++++++++++++++++++++++++++++
>> drivers/md/bcache/btree.h |  1 +
>> drivers/md/bcache/super.c | 15 ++++++++++++++-
>> 3 files changed, 50 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
>> index e136d6edc1ed..a5d54af73111 100644
>> --- a/drivers/md/bcache/btree.c
>> +++ b/drivers/md/bcache/btree.c
>> @@ -2755,6 +2755,41 @@ struct keybuf_key *bch_keybuf_next_rescan(struct cache_set *c,
>> 	return ret;
>> }
>>
>> +static bool check_pred(struct keybuf *buf, struct bkey *k)
>> +{
>> +	return true;
>> +}
>> +
>> +bool bch_btree_can_inode_reuse(struct cache_set *c, size_t inode)
>> +{
>> +	bool ret = true;
>> +	struct keybuf_key *k;
>> +	struct bkey end_key = KEY(inode, MAX_KEY_OFFSET, 0);
>> +	struct keybuf *keys = kzalloc(sizeof(struct keybuf), GFP_KERNEL);
>> +
>> +	if (!keys) {
>> +		ret = false;
>> +		goto out;
>> +	}
>> +
>> +	bch_keybuf_init(keys);
>> +	keys->last_scanned = KEY(inode, 0, 0);
>> +
>> +	while (ret) {
>> +		k = bch_keybuf_next_rescan(c, keys, &end_key, check_pred);
>> +		if (!k)
>
> This is a single thread iteration, for a large filled cache device it can be very slow. I observed 40+ minutes during my testing.
>
>
> Coly Li
>
Hi, Coly
We first use the zero_uuid slot, and reuse only if there is no zero_uuid 
slot. This is just an imperfect solution to make bcache available, so we 
haven't tested its performance. We think we will eventually need to 
actively clean up these bkeys in a new thread and reset the invalid_uuid 
to zero_uuid.
mingzhe
>
>> +			break;
>> +
>> +		if (KEY_INODE(&k->key) == inode)
>> +			ret = false;
>> +		bch_keybuf_del(keys, k);
>> +	}
>> +
>> +	kfree(keys);
>> +out:
>> +	return ret;
>> +}
>> +
>> void bch_keybuf_init(struct keybuf *buf)
>> {
>> 	buf->last_scanned	= MAX_KEY;
>> diff --git a/drivers/md/bcache/btree.h b/drivers/md/bcache/btree.h
>> index 1b5fdbc0d83e..c3e6094adb62 100644
>> --- a/drivers/md/bcache/btree.h
>> +++ b/drivers/md/bcache/btree.h
>> @@ -413,4 +413,5 @@ struct keybuf_key *bch_keybuf_next_rescan(struct cache_set *c,
>> 					  struct bkey *end,
>> 					  keybuf_pred_fn *pred);
>> void bch_update_bucket_in_use(struct cache_set *c, struct gc_stat *stats);
>> +bool bch_btree_can_inode_reuse(struct cache_set *c, size_t inode);
>> #endif
>> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>> index 3563d15dbaf2..31f7aa347561 100644
>> --- a/drivers/md/bcache/super.c
>> +++ b/drivers/md/bcache/super.c
>> @@ -544,11 +544,24 @@ static struct uuid_entry *uuid_find(struct cache_set *c, const char *uuid)
>> 	return NULL;
>> }
>>
>> +static struct uuid_entry *uuid_find_reuse(struct cache_set *c)
>> +{
>> +	struct uuid_entry *u;
>> +
>> +	for (u = c->uuids; u < c->uuids + c->nr_uuids; u++)
>> +		if (!memcmp(u->uuid, invalid_uuid, 16) &&
>> +		    bch_btree_can_inode_reuse(c, u - c->uuids))
>> +			return u;
>> +
>> +	return NULL;
>> +}
>> +
>> static struct uuid_entry *uuid_find_empty(struct cache_set *c)
>> {
>> 	static const char zero_uuid[16] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
>> +	struct uuid_entry *u = uuid_find(c, zero_uuid);
>>
>> -	return uuid_find(c, zero_uuid);
>> +	return u ? u : uuid_find_reuse(c);
>> }
>>
>> /*
>> -- 
>> 2.17.1
>>
>