linux-kernel - [PATCH RFC 4/6] dcache: stop walking siblings if remaining dentries all negative

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Date:   Thu, 21 Jan 2021 18:49:43 +0530
From:   Gautham Ananthakrishna <gautham.ananthakrishna@...cle.com>
To:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org
Cc:     viro@...iv.linux.org.uk, matthew.wilcox@...cle.com,
        khlebnikov@...dex-team.ru, gautham.ananthakrishna@...cle.com
Subject: [PATCH RFC 4/6] dcache: stop walking siblings if remaining dentries all negative

From: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>

Most walkers are interested only in positive dentries.

Changes in simple_* libfs helpers are mostly cosmetic: it shouldn't cache
negative dentries unless uses d_delete other than always_delete_dentry().

Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Signed-off-by: Gautham Ananthakrishna <gautham.ananthakrishna@...cle.com>
---
 fs/dcache.c | 9 +++++++++
 fs/libfs.c  | 3 +++
 2 files changed, 12 insertions(+)

diff --git a/fs/dcache.c b/fs/dcache.c
index 894e6da..492a42f 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1459,6 +1459,8 @@ static enum d_walk_ret path_check_mount(void *data, struct dentry *dentry)
 	struct check_mount *info = data;
 	struct path path = { .mnt = info->mnt, .dentry = dentry };
 
+	if (d_is_tail_negative(dentry))
+		return D_WALK_SKIP_SIBLINGS;
 	if (likely(!d_mountpoint(dentry)))
 		return D_WALK_CONTINUE;
 	if (__path_is_mountpoint(&path)) {
@@ -1705,6 +1707,10 @@ void shrink_dcache_for_umount(struct super_block *sb)
 static enum d_walk_ret find_submount(void *_data, struct dentry *dentry)
 {
 	struct dentry **victim = _data;
+
+	if (d_is_tail_negative(dentry))
+		return D_WALK_SKIP_SIBLINGS;
+
 	if (d_mountpoint(dentry)) {
 		__dget_dlock(dentry);
 		*victim = dentry;
@@ -3174,6 +3180,9 @@ static enum d_walk_ret d_genocide_kill(void *data, struct dentry *dentry)
 {
 	struct dentry *root = data;
 	if (dentry != root) {
+		if (d_is_tail_negative(dentry))
+			return D_WALK_SKIP_SIBLINGS;
+
 		if (d_unhashed(dentry) || !dentry->d_inode)
 			return D_WALK_SKIP;
 
diff --git a/fs/libfs.c b/fs/libfs.c
index 7124c2e..15d5ecf 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -410,6 +410,9 @@ int simple_empty(struct dentry *dentry)
 
 	spin_lock(&dentry->d_lock);
 	list_for_each_entry(child, &dentry->d_subdirs, d_child) {
+		if (d_is_tail_negative(child))
+			break;
+
 		spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
 		if (simple_positive(child)) {
 			spin_unlock(&child->d_lock);
-- 
1.8.3.1