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| author | Al Viro <viro@zeniv.linux.org.uk> | 2009-06-24 02:05:18 -0400 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2009-06-24 08:15:25 -0400 |
| commit | c63e09ecccb50f930e899d7005edc5411ee86d4f (patch) | |
| tree | aafa5169cde98a2bb8327fcc948c76dba0746322 /fs/super.c | |
| parent | 7e325d3a6b117c7288bfc0755410e9d9d2b71326 (diff) | |
| download | lwn-c63e09ecccb50f930e899d7005edc5411ee86d4f.tar.gz lwn-c63e09ecccb50f930e899d7005edc5411ee86d4f.zip | |
Make allocation of anon devices cheaper
Standard trick - add a new variable (start) such that
for each n < start n is known to be busy. Allocation can
skip checking everything in [0..start) and if it returns
n, we can set start to n + 1. Freeing below start sets
start to what we'd just freed.
Of course, it still sucks if we do something like
free 0
allocate
allocate
in a loop - still O(n^2) time. However, on saner loads it
improves the things a lot and the entire thing is not worth
the trouble of switching to something with better worst-case
behaviour.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/super.c')
| -rw-r--r-- | fs/super.c | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/fs/super.c b/fs/super.c index d40d53a22fb5..808ffd59e01b 100644 --- a/fs/super.c +++ b/fs/super.c @@ -608,6 +608,7 @@ void emergency_remount(void) static DEFINE_IDA(unnamed_dev_ida); static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */ +static int unnamed_dev_start = 0; /* don't bother trying below it */ int set_anon_super(struct super_block *s, void *data) { @@ -618,7 +619,8 @@ int set_anon_super(struct super_block *s, void *data) if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0) return -ENOMEM; spin_lock(&unnamed_dev_lock); - error = ida_get_new(&unnamed_dev_ida, &dev); + error = ida_get_new_above(&unnamed_dev_ida, unnamed_dev_start, &dev); + unnamed_dev_start = dev + 1; spin_unlock(&unnamed_dev_lock); if (error == -EAGAIN) /* We raced and lost with another CPU. */ @@ -629,6 +631,7 @@ int set_anon_super(struct super_block *s, void *data) if ((dev & MAX_ID_MASK) == (1 << MINORBITS)) { spin_lock(&unnamed_dev_lock); ida_remove(&unnamed_dev_ida, dev); + unnamed_dev_start = dev; spin_unlock(&unnamed_dev_lock); return -EMFILE; } @@ -645,6 +648,8 @@ void kill_anon_super(struct super_block *sb) generic_shutdown_super(sb); spin_lock(&unnamed_dev_lock); ida_remove(&unnamed_dev_ida, slot); + if (slot < unnamed_dev_start) + unnamed_dev_start = slot; spin_unlock(&unnamed_dev_lock); } |