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Date: Sat, 10 Oct 2015 00:18:04 +0800
From: Minfei Huang <mhuang@...hat.com>
To: yalin wang <yalin.wang2010@...il.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
On 09/28/15 at 02:52pm, yalin wang wrote:
> 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;
If we should copy the successive struct buffer_head, it is appropriate
to use memcpy to copy a bunch of struct buffer_head.
Thanks
Minfei
> }
> }
> - 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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