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Date: Mon, 28 Sep 2015 14:52:51 +0800
From: yalin wang <yalin.wang2010@...il.com>
To: Minfei Huang <mhuang@...hat.com>
Cc: Al Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, Minfei Huang <mnfhuang@...il.com>
Subject: Re: [PATCH] fs/buffer: simplify the code flow of LRU management algorithm
why not change like this:
diff --git a/fs/buffer.c b/fs/buffer.c
index 82283ab..d6769f1 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1287,40 +1287,31 @@ static inline void check_irqs_on(void)
*/
static void bh_lru_install(struct buffer_head *bh)
{
- struct buffer_head *evictee = NULL;
+ struct buffer_head *old = NULL;
check_irqs_on();
bh_lru_lock();
if (__this_cpu_read(bh_lrus.bhs[0]) != bh) {
- struct buffer_head *bhs[BH_LRU_SIZE];
- int in;
+ struct buffer_head *temp;
int out = 0;
+ old = __this_cpu_read(bh_lrus.bhs[0]);
get_bh(bh);
- bhs[out++] = bh;
- for (in = 0; in < BH_LRU_SIZE; in++) {
- struct buffer_head *bh2 =
- __this_cpu_read(bh_lrus.bhs[in]);
-
- if (bh2 == bh) {
- __brelse(bh2);
+ __this_cpu_write(bh_lrus.bhs[out++], bh);
+ for (; out < BH_LRU_SIZE; out++) {
+ if (old == bh || old == NULL) {
+ break;
} else {
- if (out >= BH_LRU_SIZE) {
- BUG_ON(evictee != NULL);
- evictee = bh2;
- } else {
- bhs[out++] = bh2;
- }
+ temp = __this_cpu_read(bh_lrus.bhs[out]);
+ __this_cpu_write(bh_lrus.bhs[out], old);
+ old = temp;
}
}
- while (out < BH_LRU_SIZE)
- bhs[out++] = NULL;
- memcpy(this_cpu_ptr(&bh_lrus.bhs), bhs, sizeof(bhs));
}
bh_lru_unlock();
- if (evictee)
- __brelse(evictee);
+ if (old)
+ __brelse(old);
}
/*
more simple to understand and have better performance .
am i understanding correctly ?
> On Sep 28, 2015, at 13:36, Minfei Huang <mhuang@...hat.com> wrote:
>
> 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@...il.com>
>>
>> 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@...il.com>
>> ---
>> 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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