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Commit 312d3ca8 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Al Viro
Browse files

fs: use percpu counter for nr_dentry and nr_dentry_unused 



The nr_dentry stat is a globally touched cacheline and atomic operation
twice over the lifetime of a dentry. It is used for the benfit of userspace
only. Turn it into a per-cpu counter and always decrement it in d_free instead
of doing various batching operations to reduce lock hold times in the callers.

Based on an earlier patch from Nick Piggin <npiggin@suse.de>.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 9c82ab9c

fs/dcache.c

+32 −19
Original line number Diff line number Diff line
@@ -67,6 +67,19 @@ struct dentry_stat_t dentry_stat = { 
	.age_limit = 45,

};



static struct percpu_counter nr_dentry __cacheline_aligned_in_smp;

static struct percpu_counter nr_dentry_unused __cacheline_aligned_in_smp;



#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)

int proc_nr_dentry(ctl_table *table, int write, void __user *buffer,

		   size_t *lenp, loff_t *ppos)

{

	dentry_stat.nr_dentry = percpu_counter_sum_positive(&nr_dentry);

	dentry_stat.nr_unused = percpu_counter_sum_positive(&nr_dentry_unused);

	return proc_dointvec(table, write, buffer, lenp, ppos);

}

#endif



static void __d_free(struct rcu_head *head)

{

	struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
@@ -78,13 +91,14 @@ static void __d_free(struct rcu_head *head) 
}



/*

 * no dcache_lock, please.  The caller must decrement dentry_stat.nr_dentry

 * inside dcache_lock.

 * no dcache_lock, please.

 */

static void d_free(struct dentry *dentry)

{

	percpu_counter_dec(&nr_dentry);

	if (dentry->d_op && dentry->d_op->d_release)

		dentry->d_op->d_release(dentry);



	/* if dentry was never inserted into hash, immediate free is OK */

	if (hlist_unhashed(&dentry->d_hash))

		__d_free(&dentry->d_u.d_rcu);
@@ -125,14 +139,14 @@ static void dentry_lru_add(struct dentry *dentry) 
{

	list_add(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);

	dentry->d_sb->s_nr_dentry_unused++;

	dentry_stat.nr_unused++;

	percpu_counter_inc(&nr_dentry_unused);

}



static void dentry_lru_add_tail(struct dentry *dentry)

{

	list_add_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);

	dentry->d_sb->s_nr_dentry_unused++;

	dentry_stat.nr_unused++;

	percpu_counter_inc(&nr_dentry_unused);

}



static void dentry_lru_del(struct dentry *dentry)
@@ -140,7 +154,7 @@ static void dentry_lru_del(struct dentry *dentry) 
	if (!list_empty(&dentry->d_lru)) {

		list_del(&dentry->d_lru);

		dentry->d_sb->s_nr_dentry_unused--;

		dentry_stat.nr_unused--;

		percpu_counter_dec(&nr_dentry_unused);

	}

}
@@ -149,7 +163,7 @@ static void dentry_lru_del_init(struct dentry *dentry) 
	if (likely(!list_empty(&dentry->d_lru))) {

		list_del_init(&dentry->d_lru);

		dentry->d_sb->s_nr_dentry_unused--;

		dentry_stat.nr_unused--;

		percpu_counter_dec(&nr_dentry_unused);

	}

}
@@ -168,7 +182,6 @@ static struct dentry *d_kill(struct dentry *dentry) 
	struct dentry *parent;



	list_del(&dentry->d_u.d_child);

	dentry_stat.nr_dentry--;	/* For d_free, below */

	/*drops the locks, at that point nobody can reach this dentry */

	dentry_iput(dentry);

	if (IS_ROOT(dentry))
@@ -314,7 +327,6 @@ int d_invalidate(struct dentry * dentry) 
EXPORT_SYMBOL(d_invalidate);



/* This should be called _only_ with dcache_lock held */



static inline struct dentry * __dget_locked(struct dentry *dentry)

{

	atomic_inc(&dentry->d_count);
@@ -534,7 +546,7 @@ static void prune_dcache(int count) 
{

	struct super_block *sb, *p = NULL;

	int w_count;

	int unused = dentry_stat.nr_unused;

	int unused = percpu_counter_sum_positive(&nr_dentry_unused);

	int prune_ratio;

	int pruned;
@@ -699,20 +711,13 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry) 
			 * otherwise we ascend to the parent and move to the

			 * next sibling if there is one */

			if (!parent)

				goto out;



				return;

			dentry = parent;



		} while (list_empty(&dentry->d_subdirs));



		dentry = list_entry(dentry->d_subdirs.next,

				    struct dentry, d_u.d_child);

	}

out:

	/* several dentries were freed, need to correct nr_dentry */

	spin_lock(&dcache_lock);

	dentry_stat.nr_dentry -= detached;

	spin_unlock(&dcache_lock);

}



/*
@@ -896,12 +901,16 @@ EXPORT_SYMBOL(shrink_dcache_parent); 
 */

static int shrink_dcache_memory(struct shrinker *shrink, int nr, gfp_t gfp_mask)

{

	int nr_unused;



	if (nr) {

		if (!(gfp_mask & __GFP_FS))

			return -1;

		prune_dcache(nr);

	}

	return (dentry_stat.nr_unused / 100) * sysctl_vfs_cache_pressure;



	nr_unused = percpu_counter_sum_positive(&nr_dentry_unused);

	return (nr_unused / 100) * sysctl_vfs_cache_pressure;

}



static struct shrinker dcache_shrinker = {
@@ -968,9 +977,10 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name) 
	spin_lock(&dcache_lock);

	if (parent)

		list_add(&dentry->d_u.d_child, &parent->d_subdirs);

	dentry_stat.nr_dentry++;

	spin_unlock(&dcache_lock);



	percpu_counter_inc(&nr_dentry);



	return dentry;

}

EXPORT_SYMBOL(d_alloc);
@@ -2417,6 +2427,9 @@ static void __init dcache_init(void) 
{

	int loop;



	percpu_counter_init(&nr_dentry, 0);

	percpu_counter_init(&nr_dentry_unused, 0);



	/* 

	 * A constructor could be added for stable state like the lists,

	 * but it is probably not worth it because of the cache nature

include/linux/fs.h

+2 −0
Original line number Diff line number Diff line
@@ -2490,6 +2490,8 @@ ssize_t simple_attr_write(struct file *file, const char __user *buf, 
struct ctl_table;

int proc_nr_files(struct ctl_table *table, int write,

		  void __user *buffer, size_t *lenp, loff_t *ppos);

int proc_nr_dentry(struct ctl_table *table, int write,

		  void __user *buffer, size_t *lenp, loff_t *ppos);

int proc_nr_inodes(struct ctl_table *table, int write,

		   void __user *buffer, size_t *lenp, loff_t *ppos);

int __init get_filesystem_list(char *buf);

kernel/sysctl.c

+1 −1
Original line number Diff line number Diff line
@@ -1377,7 +1377,7 @@ static struct ctl_table fs_table[] = { 
		.data		= &dentry_stat,

		.maxlen		= 6*sizeof(int),

		.mode		= 0444,

		.proc_handler	= proc_dointvec,

		.proc_handler	= proc_nr_dentry,

	},

	{

		.procname	= "overflowuid",