Commit 23044507 authored by Nick Piggin's avatar Nick Piggin
Browse files

fs: dcache scale lru 



Add a new lock, dcache_lru_lock, to protect the dcache LRU list from concurrent
modification. d_lru is also protected by d_lock, which allows LRU lists to be
accessed without the lru lock, using RCU in future patches.

Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
parent 789680d1

fs/dcache.c

+84 −28
Original line number Diff line number Diff line
@@ -37,11 +37,19 @@ 


/*

 * Usage:

 * dcache_hash_lock protects dcache hash table, s_anon lists

 * dcache_hash_lock protects:

 *   - the dcache hash table, s_anon lists

 * dcache_lru_lock protects:

 *   - the dcache lru lists and counters

 * d_lock protects:

 *   - d_flags

 *   - d_name

 *   - d_lru

 *

 * Ordering:

 * dcache_lock

 *   dentry->d_lock

 *     dcache_lru_lock

 *     dcache_hash_lock

 *

 * if (dentry1 < dentry2)
@@ -52,6 +60,7 @@ int sysctl_vfs_cache_pressure __read_mostly = 100; 
EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);



static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_hash_lock);

static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lru_lock);

__cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lock);

__cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
@@ -154,28 +163,38 @@ static void dentry_iput(struct dentry * dentry) 
}



/*

 * dentry_lru_(add|del|move_tail) must be called with dcache_lock held.

 * dentry_lru_(add|del|move_tail) must be called with d_lock held.

 */

static void dentry_lru_add(struct dentry *dentry)

{

	if (list_empty(&dentry->d_lru)) {

		spin_lock(&dcache_lru_lock);

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

		dentry->d_sb->s_nr_dentry_unused++;

		dentry_stat.nr_unused++;

		spin_unlock(&dcache_lru_lock);

	}

}



static void dentry_lru_del(struct dentry *dentry)

static void __dentry_lru_del(struct dentry *dentry)

{

	if (!list_empty(&dentry->d_lru)) {

	list_del_init(&dentry->d_lru);

	dentry->d_sb->s_nr_dentry_unused--;

	dentry_stat.nr_unused--;

}



static void dentry_lru_del(struct dentry *dentry)

{

	if (!list_empty(&dentry->d_lru)) {

		spin_lock(&dcache_lru_lock);

		__dentry_lru_del(dentry);

		spin_unlock(&dcache_lru_lock);

	}

}



static void dentry_lru_move_tail(struct dentry *dentry)

{

	spin_lock(&dcache_lru_lock);

	if (list_empty(&dentry->d_lru)) {

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

		dentry->d_sb->s_nr_dentry_unused++;
@@ -183,6 +202,7 @@ static void dentry_lru_move_tail(struct dentry *dentry) 
	} else {

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

	}

	spin_unlock(&dcache_lru_lock);

}



/**
@@ -192,6 +212,8 @@ static void dentry_lru_move_tail(struct dentry *dentry) 
 * The dentry must already be unhashed and removed from the LRU.

 *

 * If this is the root of the dentry tree, return NULL.

 *

 * dcache_lock and d_lock must be held by caller, are dropped by d_kill.

 */

static struct dentry *d_kill(struct dentry *dentry)

	__releases(dentry->d_lock)
@@ -383,10 +405,19 @@ 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_dlock(struct dentry *dentry)

{

	atomic_inc(&dentry->d_count);

	dentry_lru_del(dentry);

	return dentry;

}



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

{

	atomic_inc(&dentry->d_count);

	spin_lock(&dentry->d_lock);

	dentry_lru_del(dentry);

	spin_unlock(&dentry->d_lock);

	return dentry;

}
@@ -465,7 +496,7 @@ restart: 
	list_for_each_entry(dentry, &inode->i_dentry, d_alias) {

		spin_lock(&dentry->d_lock);

		if (!atomic_read(&dentry->d_count)) {

			__dget_locked(dentry);

			__dget_locked_dlock(dentry);

			__d_drop(dentry);

			spin_unlock(&dentry->d_lock);

			spin_unlock(&dcache_lock);
@@ -489,7 +520,6 @@ EXPORT_SYMBOL(d_prune_aliases); 
static void prune_one_dentry(struct dentry * dentry)

	__releases(dentry->d_lock)

	__releases(dcache_lock)

	__acquires(dcache_lock)

{

	__d_drop(dentry);

	dentry = d_kill(dentry);
@@ -498,15 +528,16 @@ static void prune_one_dentry(struct dentry * dentry) 
	 * Prune ancestors.  Locking is simpler than in dput(),

	 * because dcache_lock needs to be taken anyway.

	 */

	spin_lock(&dcache_lock);

	while (dentry) {

		if (!atomic_dec_and_lock(&dentry->d_count, &dentry->d_lock))

		spin_lock(&dcache_lock);

		if (!atomic_dec_and_lock(&dentry->d_count, &dentry->d_lock)) {

			spin_unlock(&dcache_lock);

			return;

		}



		dentry_lru_del(dentry);

		__d_drop(dentry);

		dentry = d_kill(dentry);

		spin_lock(&dcache_lock);

	}

}
@@ -516,21 +547,31 @@ static void shrink_dentry_list(struct list_head *list) 


	while (!list_empty(list)) {

		dentry = list_entry(list->prev, struct dentry, d_lru);

		dentry_lru_del(dentry);



		if (!spin_trylock(&dentry->d_lock)) {

			spin_unlock(&dcache_lru_lock);

			cpu_relax();

			spin_lock(&dcache_lru_lock);

			continue;

		}



		__dentry_lru_del(dentry);



		/*

		 * We found an inuse dentry which was not removed from

		 * the LRU because of laziness during lookup.  Do not free

		 * it - just keep it off the LRU list.

		 */

		spin_lock(&dentry->d_lock);

		if (atomic_read(&dentry->d_count)) {

			spin_unlock(&dentry->d_lock);

			continue;

		}

		spin_unlock(&dcache_lru_lock);



		prune_one_dentry(dentry);

		/* dentry->d_lock was dropped in prune_one_dentry() */

		cond_resched_lock(&dcache_lock);

		/* dcache_lock and dentry->d_lock dropped */

		spin_lock(&dcache_lock);

		spin_lock(&dcache_lru_lock);

	}

}
@@ -551,32 +592,36 @@ static void __shrink_dcache_sb(struct super_block *sb, int *count, int flags) 
	int cnt = *count;



	spin_lock(&dcache_lock);

relock:

	spin_lock(&dcache_lru_lock);

	while (!list_empty(&sb->s_dentry_lru)) {

		dentry = list_entry(sb->s_dentry_lru.prev,

				struct dentry, d_lru);

		BUG_ON(dentry->d_sb != sb);



		if (!spin_trylock(&dentry->d_lock)) {

			spin_unlock(&dcache_lru_lock);

			cpu_relax();

			goto relock;

		}



		/*

		 * If we are honouring the DCACHE_REFERENCED flag and the

		 * dentry has this flag set, don't free it.  Clear the flag

		 * and put it back on the LRU.

		 */

		if (flags & DCACHE_REFERENCED) {

			spin_lock(&dentry->d_lock);

			if (dentry->d_flags & DCACHE_REFERENCED) {

		if (flags & DCACHE_REFERENCED &&

				dentry->d_flags & DCACHE_REFERENCED) {

			dentry->d_flags &= ~DCACHE_REFERENCED;

			list_move(&dentry->d_lru, &referenced);

			spin_unlock(&dentry->d_lock);

				cond_resched_lock(&dcache_lock);

				continue;

			}

			spin_unlock(&dentry->d_lock);

		}



		} else {

			list_move_tail(&dentry->d_lru, &tmp);

			spin_unlock(&dentry->d_lock);

			if (!--cnt)

				break;

		cond_resched_lock(&dcache_lock);

		}

		/* XXX: re-add cond_resched_lock when dcache_lock goes away */

	}



	*count = cnt;
@@ -584,6 +629,7 @@ static void __shrink_dcache_sb(struct super_block *sb, int *count, int flags) 


	if (!list_empty(&referenced))

		list_splice(&referenced, &sb->s_dentry_lru);

	spin_unlock(&dcache_lru_lock);

	spin_unlock(&dcache_lock);



}
@@ -679,10 +725,12 @@ void shrink_dcache_sb(struct super_block *sb) 
	LIST_HEAD(tmp);



	spin_lock(&dcache_lock);

	spin_lock(&dcache_lru_lock);

	while (!list_empty(&sb->s_dentry_lru)) {

		list_splice_init(&sb->s_dentry_lru, &tmp);

		shrink_dentry_list(&tmp);

	}

	spin_unlock(&dcache_lru_lock);

	spin_unlock(&dcache_lock);

}

EXPORT_SYMBOL(shrink_dcache_sb);
@@ -701,7 +749,9 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry) 


	/* detach this root from the system */

	spin_lock(&dcache_lock);

	spin_lock(&dentry->d_lock);

	dentry_lru_del(dentry);

	spin_unlock(&dentry->d_lock);

	__d_drop(dentry);

	spin_unlock(&dcache_lock);
@@ -715,7 +765,9 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry) 
			spin_lock(&dcache_lock);

			list_for_each_entry(loop, &dentry->d_subdirs,

					    d_u.d_child) {

				spin_lock(&loop->d_lock);

				dentry_lru_del(loop);

				spin_unlock(&loop->d_lock);

				__d_drop(loop);

				cond_resched_lock(&dcache_lock);

			}
@@ -892,6 +944,8 @@ resume: 
		struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);

		next = tmp->next;



		spin_lock(&dentry->d_lock);



		/* 

		 * move only zero ref count dentries to the end 

		 * of the unused list for prune_dcache
@@ -903,6 +957,8 @@ resume: 
			dentry_lru_del(dentry);

		}



		spin_unlock(&dentry->d_lock);



		/*

		 * We can return to the caller if we have found some (this

		 * ensures forward progress). We'll be coming back to find

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