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From: Eric Sandeen on 21 Jul 2010 10:10
Wang Sheng-Hui wrote:
> Sorry. regerated the patch, please check it.
> I wrapped most code in single pair of spinlock ops for 2 reasons:
> 1) get spinlock 2 times seems time consuming
> 2) use single pair of spinlock ops can keep "count"
> consistent for the shrink operation. 2 pairs may
> get some new ces created by other processes.
>

Sorry, this patch appears to have whitespace cut & paste mangling.

More comments below.

> Signed-off-by: Wang Sheng-Hui <crosslonelyover(a)gmail.com>
> ---
> fs/mbcache.c | 24 ++++++++++++------------
> 1 files changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/fs/mbcache.c b/fs/mbcache.c
> index ec88ff3..ee57aa3 100644
> --- a/fs/mbcache.c
> +++ b/fs/mbcache.c
> @@ -201,21 +201,15 @@ mb_cache_shrink_fn(int nr_to_scan, gfp_t gfp_mask)
> {
> LIST_HEAD(free_list);
> struct list_head *l, *ltmp;
> + struct mb_cache *cache;
> int count = 0;
>
> - spin_lock(&mb_cache_spinlock);
> - list_for_each(l, &mb_cache_list) {
> - struct mb_cache *cache =
> - list_entry(l, struct mb_cache, c_cache_list);
> - mb_debug("cache %s (%d)", cache->c_name,
> - atomic_read(&cache->c_entry_count));
> - count += atomic_read(&cache->c_entry_count);
> - }
> mb_debug("trying to free %d entries", nr_to_scan);
> - if (nr_to_scan == 0) {
> - spin_unlock(&mb_cache_spinlock);
> +
> + spin_lock(&mb_cache_spinlock);
> + if (nr_to_scan == 0)
> goto out;
> - }
> +
> while (nr_to_scan-- && !list_empty(&mb_cache_lru_list)) {
> struct mb_cache_entry *ce =
> list_entry(mb_cache_lru_list.next,
> @@ -223,12 +217,18 @@ mb_cache_shrink_fn(int nr_to_scan, gfp_t gfp_mask)
> list_move_tail(&ce->e_lru_list, &free_list);
> __mb_cache_entry_unhash(ce);
> }
> - spin_unlock(&mb_cache_spinlock);

you can't do this because

> list_for_each_safe(l, ltmp, &free_list) {
> __mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,

this takes the spinlock too and you'll deadlock.

Did you test this patch?

-Eric

> e_lru_list), gfp_mask);
> }
> out:
> + list_for_each_entry(cache, &mb_cache_list, c_cache_list) {
> + mb_debug("cache %s (%d)", cache->c_name,
> + atomic_read(&cache->c_entry_count));
> + count += atomic_read(&cache->c_entry_count);
> + }
> + spin_unlock(&mb_cache_spinlock);
> +
> return (count / 100) * sysctl_vfs_cache_pressure;
> }
>

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From: Wang Sheng-Hui on 21 Jul 2010 21:00
Sorry, missed that. Regerated and passed checkpatch.pl check.
Please check it.


Signed-off-by: Wang Sheng-Hui <crosslonelyover(a)gmail.com>
---
fs/mbcache.c | 23 ++++++++++++-----------
1 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/fs/mbcache.c b/fs/mbcache.c
index ec88ff3..603170e 100644
--- a/fs/mbcache.c
+++ b/fs/mbcache.c
@@ -201,21 +201,14 @@ mb_cache_shrink_fn(int nr_to_scan, gfp_t gfp_mask)
{
LIST_HEAD(free_list);
struct list_head *l, *ltmp;
+ struct mb_cache *cache;
int count = 0;

- spin_lock(&mb_cache_spinlock);
- list_for_each(l, &mb_cache_list) {
- struct mb_cache *cache =
- list_entry(l, struct mb_cache, c_cache_list);
- mb_debug("cache %s (%d)", cache->c_name,
- atomic_read(&cache->c_entry_count));
- count += atomic_read(&cache->c_entry_count);
- }
mb_debug("trying to free %d entries", nr_to_scan);
- if (nr_to_scan == 0) {
- spin_unlock(&mb_cache_spinlock);
+ if (nr_to_scan == 0)
goto out;
- }
+
+ spin_lock(&mb_cache_spinlock);
while (nr_to_scan-- && !list_empty(&mb_cache_lru_list)) {
struct mb_cache_entry *ce =
list_entry(mb_cache_lru_list.next,
@@ -229,6 +222,14 @@ mb_cache_shrink_fn(int nr_to_scan, gfp_t gfp_mask)
e_lru_list), gfp_mask);
}
out:
+ spin_lock(&mb_cache_spinlock);
+ list_for_each_entry(cache, &mb_cache_list, c_cache_list) {
+ mb_debug("cache %s (%d)", cache->c_name,
+ atomic_read(&cache->c_entry_count));
+ count += atomic_read(&cache->c_entry_count);
+ }
+ spin_unlock(&mb_cache_spinlock);
+
return (count / 100) * sysctl_vfs_cache_pressure;
}

--
1.6.3.3
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