2009-09-04 06:58:45

by Nick Piggin

Subject: [patch 08/33] fs: dcache scale nr_dentry

Make dentry_stat_t.nr_dentry an atomic_t type, and move it from under
dcache_lock.
---
fs/dcache.c | 20 +++++++++-----------
include/linux/dcache.h | 4 ++--
kernel/sysctl.c | 6 ++++++
3 files changed, 17 insertions(+), 13 deletions(-)

Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c
+++ linux-2.6/fs/dcache.c
@@ -83,6 +83,7 @@ static struct hlist_head *dentry_hashtab

/* Statistics gathering. */
struct dentry_stat_t dentry_stat = {
+ .nr_dentry = ATOMIC_INIT(0),
.age_limit = 45,
};

@@ -101,11 +102,11 @@ static void d_callback(struct rcu_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)
{
+ atomic_dec(&dentry_stat.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 */
@@ -212,7 +213,6 @@ static struct dentry *d_kill(struct dent
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))
@@ -777,10 +777,7 @@ static void shrink_dcache_for_umount_sub
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);
+ return;
}

/*
@@ -1035,11 +1032,12 @@ struct dentry *d_alloc(struct dentry * p
INIT_LIST_HEAD(&dentry->d_u.d_child);
}

- spin_lock(&dcache_lock);
- if (parent)
+ if (parent) {
+ spin_lock(&dcache_lock);
list_add(&dentry->d_u.d_child, &parent->d_subdirs);
- dentry_stat.nr_dentry++;
- spin_unlock(&dcache_lock);
+ spin_unlock(&dcache_lock);
+ }
+ atomic_inc(&dentry_stat.nr_dentry);

return dentry;
}
Index: linux-2.6/include/linux/dcache.h
===================================================================
--- linux-2.6.orig/include/linux/dcache.h
+++ linux-2.6/include/linux/dcache.h
@@ -37,8 +37,8 @@ struct qstr {
};

struct dentry_stat_t {
- int nr_dentry;
- int nr_unused;
+ atomic_t nr_dentry;
+ int nr_unused; /* protected by dcache_lru_lock */
int age_limit; /* age in seconds */
int want_pages; /* pages requested by system */
int dummy[2];
Index: linux-2.6/kernel/sysctl.c
===================================================================
--- linux-2.6.orig/kernel/sysctl.c
+++ linux-2.6/kernel/sysctl.c
@@ -1413,6 +1413,12 @@ static struct ctl_table fs_table[] = {
.extra2 = &sysctl_nr_open_max,
},
{
+ /*
+ * dentry_stat has an atomic_t member, so this is a bit of
+ * a hack, but it works for the moment, and I won't bother
+ * changing it now because we'll probably want to change to
+ * a more scalable counter anyway.
+ */
.ctl_name = FS_DENTRY,
.procname = "dentry-state",
.data = &dentry_stat,

2009-09-04 14:41:13

by Daniel Walker

Subject: Re: [patch 08/33] fs: dcache scale nr_dentry

On Fri, 2009-09-04 at 16:51 +1000, [email protected] wrote:
> plain text document attachment (fs-dcache-scale-nr_dentry.patch)
> Make dentry_stat_t.nr_dentry an atomic_t type, and move it from under
> dcache_lock.
> ---
> fs/dcache.c | 20 +++++++++-----------
> include/linux/dcache.h | 4 ++--
> kernel/sysctl.c | 6 ++++++
> 3 files changed, 17 insertions(+), 13 deletions(-)
>

No sign off on this one..

Daniel

2009-09-07 07:36:37

by Nick Piggin

Subject: Re: [patch 08/33] fs: dcache scale nr_dentry

On Fri, Sep 04, 2009 at 07:41:02AM -0700, Daniel Walker wrote:
> On Fri, 2009-09-04 at 16:51 +1000, [email protected] wrote:
> > plain text document attachment (fs-dcache-scale-nr_dentry.patch)
> > Make dentry_stat_t.nr_dentry an atomic_t type, and move it from under
> > dcache_lock.
> > ---
> > fs/dcache.c | 20 +++++++++-----------
> > include/linux/dcache.h | 4 ++--
> > kernel/sysctl.c | 6 ++++++
> > 3 files changed, 17 insertions(+), 13 deletions(-)
> >
>
> No sign off on this one..

Ah, yeah... They're not really signoffable quality. Even a bit too
raw (not enough comments) for detailed review. I just want to get
the high level design out there again for comments because it is a
really big time investment to go further...

Just want to see if I make anyone upset or there are some bright
ideas of how to improve things :)