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btrfs: don't use slab cache for struct btrfs_delalloc_work

PATCH New David Sterba 1 participant 1 message Dec 8, 2015 Btrfs file system

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David Sterba

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PATCH 1/1 btrfs: don't use slab cache for struct btrfs_delalloc_work

Although we prefer to use separate caches for various structs, it seems better not to do that for struct btrfs_delalloc_work. Objects of this type are allocated rarely, when transaction commit calls btrfs_start_delalloc_roots, requesting delayed iputs.

The objects are temporary (with some IO involved) but still allocated and freed within __start_delalloc_inodes. Memory allocation failure is handled.

The slab cache is empty most of the time (observed on several systems), so if we need to allocate a new slab object, the first one has to allocate a full page. In a potential case of low memory conditions this might fail with higher probability compared to using the generic slab caches.

Signed-off-by David Sterba <[email protected]>
---
 fs/btrfs/inode.c | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)
fs/btrfs/inode.c +2 -12
index 994490d5fa64..eeae851427fe 100644
@@ -77,7 +77,6 @@ static const struct file_operations btrfs_dir_file_operations;
 static struct extent_io_ops btrfs_extent_io_ops;
 
 static struct kmem_cache *btrfs_inode_cachep;
-static struct kmem_cache *btrfs_delalloc_work_cachep;
 struct kmem_cache *btrfs_trans_handle_cachep;
 struct kmem_cache *btrfs_transaction_cachep;
 struct kmem_cache *btrfs_path_cachep;

@@ -9174,8 +9173,6 @@ void btrfs_destroy_cachep(void)
 		kmem_cache_destroy(btrfs_path_cachep);
 	if (btrfs_free_space_cachep)
 		kmem_cache_destroy(btrfs_free_space_cachep);
-	if (btrfs_delalloc_work_cachep)
-		kmem_cache_destroy(btrfs_delalloc_work_cachep);
 }
 
 int btrfs_init_cachep(void)

@@ -9210,13 +9207,6 @@ int btrfs_init_cachep(void)
 	if (!btrfs_free_space_cachep)
 		goto fail;
 
-	btrfs_delalloc_work_cachep = kmem_cache_create("btrfs_delalloc_work",
-			sizeof(struct btrfs_delalloc_work), 0,
-			SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD,
-			NULL);
-	if (!btrfs_delalloc_work_cachep)
-		goto fail;
-
 	return 0;
 fail:
 	btrfs_destroy_cachep();

@@ -9461,7 +9451,7 @@ struct btrfs_delalloc_work *btrfs_alloc_delalloc_work(struct inode *inode,
 {
 	struct btrfs_delalloc_work *work;
 
-	work = kmem_cache_zalloc(btrfs_delalloc_work_cachep, GFP_NOFS);
+	work = kmalloc(sizeof(*work), GFP_NOFS);
 	if (!work)
 		return NULL;
 

@@ -9480,7 +9470,7 @@ struct btrfs_delalloc_work *btrfs_alloc_delalloc_work(struct inode *inode,
 void btrfs_wait_and_free_delalloc_work(struct btrfs_delalloc_work *work)
 {
 	wait_for_completion(&work->completion);
-	kmem_cache_free(btrfs_delalloc_work_cachep, work);
+	kfree(work);
 }
 
 /*
Signature · 1 line
1.8.4.5