[PATCH RFC 6/8] dcache: stop walking siblings if remaining dentries all negative

Konstantin Khlebnikov
2020-05-08T12:23:33Z

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@yandex-team.ru>
---
fs/dcache.c | 10 ++++++++++
fs/libfs.c | 10 +++++++++-
2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 44c6832d21d6..0fd2e02e507b 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1442,6 +1442,9 @@ 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)) {
@@ -1688,6 +1691,10 @@ 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;
@@ -3159,6 +3166,9 @@ 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 3759fbacf522..de944c241cf0 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -106,6 +106,10 @@ static struct dentry *scan_positives(struct dentry *cursor,
spin_lock(&dentry->d_lock);
while ((p = p->next) != &dentry->d_subdirs) {
struct dentry *d = list_entry(p, struct dentry, d_child);
+
+ if (d_is_tail_negative(d))
+ break;
+
// we must at least skip cursors, to avoid livelocks
if (d->d_flags & DCACHE_DENTRY_CURSOR)
continue;
@@ -255,7 +259,8 @@ static struct dentry *find_next_child(struct dentry *parent, struct dentry *prev
spin_unlock(&d->d_lock);
if (likely(child))
break;
- }
+ } else if (d_is_tail_negative(d))
+ break;
}
spin_unlock(&parent->d_lock);
dput(prev);
@@ -408,6 +413,9 @@ 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);