[PATCH v2] fs, mm: account filp cache to kmemcg

[PATCH v2] fs, mm: account filp cache to kmemcg

[Shakeel Butt]

The allocations from filp cache can be directly triggered by user
space applications. A buggy application can consume a significant
amount of unaccounted system memory. Though we have not noticed
such buggy applications in our production but upon close inspection,
we found that a lot of machines spend very significant amount of
memory on these caches.

One way to limit allocations from filp cache is to set system level
limit of maximum number of open files. However this limit is shared
between different users on the system and one user can hog this
resource. To cater that, we can charge filp to kmemcg and set the
maximum limit very high and let the memory limit of each user limit
the number of files they can open and indirectly limiting their
allocations from filp cache.

One side effect of this change is that it will allow _sysctl() to
return ENOMEM and the man page of _sysctl() does not specify that.
However the man page also discourages to use _sysctl() at all.

Signed-off-by: Shakeel Butt <shakeelb@google.com>
---

Changelog since v1:
- removed names_cache charging to kmemcg

 fs/file_table.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index 61517f57f8ef..567888cdf7d3 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -312,7 +312,7 @@ void put_filp(struct file *file)
 void __init files_init(void)
 {
 	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
-			SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
+			SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT, NULL);
 	percpu_counter_init(&nr_files, 0, GFP_KERNEL);
 }
 
-- 
2.15.0.rc0.271.g36b669edcc-goog

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Re: [PATCH v2] fs, mm: account filp cache to kmemcg

[Michal Hocko]

On Wed 11-10-17 12:03:59, Shakeel Butt wrote:
> The allocations from filp cache can be directly triggered by user
> space applications. A buggy application can consume a significant
> amount of unaccounted system memory. Though we have not noticed
> such buggy applications in our production but upon close inspection,
> we found that a lot of machines spend very significant amount of
> memory on these caches.
> 
> One way to limit allocations from filp cache is to set system level
> limit of maximum number of open files. However this limit is shared
> between different users on the system and one user can hog this
> resource. To cater that, we can charge filp to kmemcg and set the
> maximum limit very high and let the memory limit of each user limit
> the number of files they can open and indirectly limiting their
> allocations from filp cache.
> 
> One side effect of this change is that it will allow _sysctl() to
> return ENOMEM and the man page of _sysctl() does not specify that.
> However the man page also discourages to use _sysctl() at all.
> 
> Signed-off-by: Shakeel Butt <shakeelb@google.com>

OK, this makes more sense than the original patch. struct file is not
really large (248B on my system) so I am not sure how much this helps
though. Anyway, I have no objections to the patch but I do not feel
qualified to ack it either.

> ---
> 
> Changelog since v1:
> - removed names_cache charging to kmemcg
> 
>  fs/file_table.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/file_table.c b/fs/file_table.c
> index 61517f57f8ef..567888cdf7d3 100644
> --- a/fs/file_table.c
> +++ b/fs/file_table.c
> @@ -312,7 +312,7 @@ void put_filp(struct file *file)
>  void __init files_init(void)
>  {
>  	filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
> -			SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
> +			SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT, NULL);
>  	percpu_counter_init(&nr_files, 0, GFP_KERNEL);
>  }
>  
> -- 
> 2.15.0.rc0.271.g36b669edcc-goog

-- 
Michal Hocko
SUSE Labs

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