On 2020/9/22 23:47, Liu Hua wrote:
> Btree spliting and garbage collection process will drop
> placeholders, which may cause cache miss collision. We can
> insert nonoverlapping bkeys with write lock. It is helpful
> for performance.
>
Could you please to explain more detais about,
- How does "Btree spliting and garbage collection process will drop
placeholders" happen?
- And how does the consequence "cache miss collision" happen?
- Do you observe performance improvement? If yes, which part is improved
and what is the performance number?
Thanks in advance.
Coly Li
> Signed-off-by: Liu Hua <liusdu@xxxxxxx>
> ---
> drivers/md/bcache/extents.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/md/bcache/extents.c b/drivers/md/bcache/extents.c
> index c809724e6571..acebe5bdb3f1 100644
> --- a/drivers/md/bcache/extents.c
> +++ b/drivers/md/bcache/extents.c
> @@ -329,6 +329,7 @@ static bool bch_extent_insert_fixup(struct btree_keys *b,
>
> uint64_t old_offset;
> unsigned int old_size, sectors_found = 0;
> + bool overlap = false;
>
> BUG_ON(!KEY_OFFSET(insert));
> BUG_ON(!KEY_SIZE(insert));
> @@ -340,15 +341,18 @@ static bool bch_extent_insert_fixup(struct btree_keys *b,
> break;
>
> if (bkey_cmp(&START_KEY(k), insert) >= 0) {
> - if (KEY_SIZE(k))
> - break;
> - else
> + if (!KEY_SIZE(k))
> continue;
> + if (replace_key && overlap == false)
> + goto out;
> + break;
> }
>
> if (bkey_cmp(k, &START_KEY(insert)) <= 0)
> continue;
>
> + overlap = true;
> +
> old_offset = KEY_START(k);
> old_size = KEY_SIZE(k);
>
>
