Re: [PATCH 3/3] Btrfs: allocate prelim_ref with a slab allocater

[Wang Shilong <wangshilong1991@gmail.com>]

> On Thu, August 08, 2013 at 07:04 (+0200), Wang Shilong wrote:
>> struct __prelim_ref is allocated and freed frequently when
>> walking backref tree, using slab allocater can not only
>> speed up allocating but also detect memory leaks.
>> 
>> Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
>> Reviewed-by: Miao Xie <miaox@cn.fujitsu.com>
>> ---
>> fs/btrfs/backref.c | 30 +++++++++++++++++++++++++-----
>> fs/btrfs/backref.h |  2 ++
>> fs/btrfs/super.c   |  8 ++++++++
>> 3 files changed, 35 insertions(+), 5 deletions(-)
>> 
>> diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
>> index f7781e6..916e4f1 100644
>> --- a/fs/btrfs/backref.c
>> +++ b/fs/btrfs/backref.c
>> @@ -119,6 +119,26 @@ struct __prelim_ref {
>> 	u64 wanted_disk_byte;
>> };
>> 
>> +static struct kmem_cache *prelim_ref_cache;
>> +
>> +int __init btrfs_prelim_ref_init(void)
>> +{
>> +	prelim_ref_cache = kmem_cache_create("btrfs_prelim_ref",
>> +					sizeof(struct __prelim_ref),
>> +					0,
>> +					SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD,
>> +					NULL);
>> +	if (!prelim_ref_cache)
>> +		return -ENOMEM;
>> +	return 0;
>> +}
>> +
>> +void btrfs_prelim_ref_exit(void)
>> +{
>> +	if (prelim_ref_cache)
>> +		kmem_cache_destroy(prelim_ref_cache);
>> +}
>> +
>> /*
>>  * the rules for all callers of this function are:
>>  * - obtaining the parent is the goal
>> @@ -165,7 +185,7 @@ static int __add_prelim_ref(struct list_head *head, u64 root_id,
>> {
>> 	struct __prelim_ref *ref;
>> 
>> -	ref = kmalloc(sizeof(*ref), gfp_mask);
>> +	ref = kmem_cache_alloc(prelim_ref_cache, gfp_mask);
>> 	if (!ref)
>> 		return -ENOMEM;
>> 
>> @@ -493,7 +513,7 @@ static void __merge_refs(struct list_head *head, int mode)
>> 			ref1->count += ref2->count;
>> 
>> 			list_del(&ref2->list);
>> -			kfree(ref2);
>> +			kmem_cache_free(prelim_ref_cache, ref2);
>> 		}
>> 
>> 	}
>> @@ -958,7 +978,7 @@ again:
>> 			}
>> 		}
>> 		list_del(&ref->list);
>> -		kfree(ref);
>> +		kmem_cache_free(prelim_ref_cache, ref);
>> 	}
>> 
>> out:
>> @@ -966,13 +986,13 @@ out:
>> 	while (!list_empty(&prefs)) {
>> 		ref = list_first_entry(&prefs, struct __prelim_ref, list);
>> 		list_del(&ref->list);
>> -		kfree(ref);
>> +		kmem_cache_free(prelim_ref_cache, ref);
>> 	}
>> 	while (!list_empty(&prefs_delayed)) {
>> 		ref = list_first_entry(&prefs_delayed, struct __prelim_ref,
>> 				       list);
>> 		list_del(&ref->list);
>> -		kfree(ref);
>> +		kmem_cache_free(prelim_ref_cache, ref);
>> 	}
>> 
>> 	return ret;
>> diff --git a/fs/btrfs/backref.h b/fs/btrfs/backref.h
>> index 8f2e767..a910b27 100644
>> --- a/fs/btrfs/backref.h
>> +++ b/fs/btrfs/backref.h
>> @@ -72,4 +72,6 @@ int btrfs_find_one_extref(struct btrfs_root *root, u64 inode_objectid,
>> 			  struct btrfs_inode_extref **ret_extref,
>> 			  u64 *found_off);
>> 
>> +int __init btrfs_prelim_ref_init(void);
>> +void btrfs_prelim_ref_exit(void);
>> #endif
>> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
>> index b64d762..de7eb3d 100644
>> --- a/fs/btrfs/super.c
>> +++ b/fs/btrfs/super.c
>> @@ -56,6 +56,7 @@
>> #include "rcu-string.h"
>> #include "dev-replace.h"
>> #include "free-space-cache.h"
>> +#include "backref.h"
>> 
>> #define CREATE_TRACE_POINTS
>> #include <trace/events/btrfs.h>
>> @@ -1774,6 +1775,10 @@ static int __init init_btrfs_fs(void)
>> 	if (err)
>> 		goto free_auto_defrag;
>> 
>> +	err = btrfs_prelim_ref_init();
>> +	if (err)
>> +		goto free_prelim_ref;
>> +
>> 	err = btrfs_interface_init();
>> 	if (err)
>> 		goto free_delayed_ref;
>> @@ -1791,6 +1796,8 @@ static int __init init_btrfs_fs(void)
>> 
>> unregister_ioctl:
>> 	btrfs_interface_exit();
>> +free_prelim_ref:
>> +	btrfs_prelim_ref_exit();
>> free_delayed_ref:
>> 	btrfs_delayed_ref_exit();
>> free_auto_defrag:
>> @@ -1817,6 +1824,7 @@ static void __exit exit_btrfs_fs(void)
>> 	btrfs_delayed_ref_exit();
>> 	btrfs_auto_defrag_exit();
>> 	btrfs_delayed_inode_exit();
>> +	btrfs_prelim_ref_exit();
>> 	ordered_data_exit();
>> 	extent_map_exit();
>> 	extent_io_exit();
>> 
> 
> I generally like the idea of using a custom cache here. What about this one?
> 
> 324 static int __resolve_indirect_refs(struct btrfs_fs_info *fs_info,
> [...]
> 367                 /* additional parents require new refs being added here */
> 368                 while ((node = ulist_next(parents, &uiter))) {
> 369                         new_ref = kmalloc(sizeof(*new_ref), GFP_NOFS);
> 
> That new_ref will also be freed with kmem_cache_free after your patch, I think.

Yeah, you are right, i just have a question, why i can not cause problems when i free
it with kmem_cahce_free during my test ~_~.


Thanks,
Wang
> 
> Thanks,
> -Jan
> --
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