Ping, Could you someone help to review this patch?
Thanks
Minfei
On 09/10/15 at 04:09pm, Minfei Huang wrote:
> From: Minfei Huang <mnfhuang@xxxxxxxxx>
>
> There is a buffer_head lru list cache in local cpu to accelerate the
> speed. The LRU management algorithm is simple enough in
> bh_lru_install().
>
> There are three situtaions we should deal with.
> 1) All/part of the lru cache is NULL.
> 2) The new buffer_head hitts the lru cache.
> 3) The new buffer_head does hit the lru cache.
>
> We put the new buffer_head at the head of lru cache, then copy the
> buffer_head from the original lru cache, and drop the spare.
>
> Signed-off-by: Minfei Huang <mnfhuang@xxxxxxxxx>
> ---
> fs/buffer.c | 32 ++++++++++++++++++++------------
> 1 file changed, 20 insertions(+), 12 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 1cf7a53..2139574 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1287,8 +1287,6 @@ static inline void check_irqs_on(void)
> */
> static void bh_lru_install(struct buffer_head *bh)
> {
> - struct buffer_head *evictee = NULL;
> -
> check_irqs_on();
> bh_lru_lock();
> if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
> @@ -1302,25 +1300,35 @@ static void bh_lru_install(struct buffer_head *bh)
> struct buffer_head *bh2 =
> __this_cpu_read(bh_lrus.bhs[in]);
>
> - if (bh2 == bh) {
> + if (bh2 == NULL) {
> + /* Rest value in bh_lrus.bhs always is NULL */
> + break;
> + } else if (bh2 == bh) {
> __brelse(bh2);
> } else {
> - if (out >= BH_LRU_SIZE) {
> - BUG_ON(evictee != NULL);
> - evictee = bh2;
> + if (out == BH_LRU_SIZE) {
> + /*
> + * this condition will be happened,
> + * only if none of entry in
> + * bh_lrus.bhs hits the new bh,
> + * so the last bh should be released.
> + */
> + BUG_ON(in != BH_LRU_SIZE - 1);
> + __brelse(bh2);
> + break;
> } else {
> bhs[out++] = bh2;
> }
> }
> }
> - while (out < BH_LRU_SIZE)
> - bhs[out++] = NULL;
> - memcpy(this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
> + /*
> + * it is fine that the value out may be smaller than
> + * BH_LRU_SIZE. The rest of the value in bh_lrus.bhs is NULL.
> + */
> + memcpy(this_cpu_ptr(&bh_lrus.bhs), bhs,
> + sizeof(struct buffer_head *) * out);
> }
> bh_lru_unlock();
> -
> - if (evictee)
> - __brelse(evictee);
> }
>
> /*
> --
> 2.1.0
>
> --
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