From: Al Viro Date: Wed, 24 Jun 2009 06:05:18 +0000 (-0400) Subject: Make allocation of anon devices cheaper X-Git-Tag: v2.6.31-rc1~13^2~17 X-Git-Url: http://ftp.safe.ca/?p=safe%2Fjmp%2Flinux-2.6;a=commitdiff_plain;h=c63e09ecccb50f930e899d7005edc5411ee86d4f 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 --- diff --git a/fs/super.c b/fs/super.c index d40d53a..808ffd5 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); }