[PATCH] fix return value for mb_cache_shrink_fn when nr_to_scan > 0

[PATCH] fix return value for mb_cache_shrink_fn when nr_to_scan > 0

[Wang Sheng-Hui]

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. 



Signed-off-by: Wang Sheng-Hui <crosslonelyover@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);
 	list_for_each_safe(l, ltmp, &free_list) {
 		__mb_cache_entry_forget(list_entry(l, struct mb_cache_entry,
 						   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;
 }
 
-- 
1.6.3.3

Re: [PATCH] fix return value for mb_cache_shrink_fn when nr_to_scan > 0

[Eric Sandeen]

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@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;
> }
> 

re: [PATCH] fix return value for mb_cache_shrink_fn when nr_to_scan > 0

[Wang Sheng-Hui]

Sorry, missed that. Regerated and passed checkpatch.pl check. 
Please check it.


Signed-off-by: Wang Sheng-Hui <crosslonelyover@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

Re: [PATCH] fix return value for mb_cache_shrink_fn when nr_to_scan > 0

[shenghui]

Sorry to trouble you all & Thanks for your instructions!
I noticed that Andreas Gruenbacher has submitted patches
on mbcache.
Please ignore mine.


-- 


Thanks and Best Regards,
shenghui