[PATCH] Remove completion from struct klist_node

[PATCH] Remove completion from struct klist_node

[Matthew Wilcox]

Removing the completion from klist_node reduces its size from 64 bytes
to 28 on x86-64.  To maintain the semantics of klist_remove(), we add
a single list of klist nodes which are pending deletion and scan them.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

 include/linux/klist.h |    2 --
 lib/klist.c           |   48 ++++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 44 insertions(+), 6 deletions(-)

diff --git a/include/linux/klist.h b/include/linux/klist.h
index 06c338e..989a335 100644
--- a/include/linux/klist.h
+++ b/include/linux/klist.h
@@ -13,7 +13,6 @@
 #define _LINUX_KLIST_H
 
 #include <linux/spinlock.h>
-#include <linux/completion.h>
 #include <linux/kref.h>
 #include <linux/list.h>
 
@@ -41,7 +40,6 @@ struct klist_node {
 	struct klist		*n_klist;
 	struct list_head	n_node;
 	struct kref		n_ref;
-	struct completion	n_removed;
 };
 
 extern void klist_add_tail(struct klist_node *n, struct klist *k);
diff --git a/lib/klist.c b/lib/klist.c
index cca37f9..2b609ee 100644
--- a/lib/klist.c
+++ b/lib/klist.c
@@ -36,7 +36,7 @@
 
 #include <linux/klist.h>
 #include <linux/module.h>
-
+#include <linux/sched.h>
 
 /**
  * klist_init - Initialize a klist structure.
@@ -77,7 +77,6 @@ static void add_tail(struct klist *k, struct klist_node *n)
 static void klist_node_init(struct klist *k, struct klist_node *n)
 {
 	INIT_LIST_HEAD(&n->n_node);
-	init_completion(&n->n_removed);
 	kref_init(&n->n_ref);
 	n->n_klist = k;
 	if (k->get)
@@ -140,12 +139,36 @@ void klist_add_before(struct klist_node *n, struct klist_node *pos)
 }
 EXPORT_SYMBOL_GPL(klist_add_before);
 
+struct klist_waiter {
+	struct klist_waiter *next;
+	struct klist_node *node;
+	struct task_struct *process;
+	int woken;
+};
+
+static DEFINE_SPINLOCK(klist_remove_lock);
+static struct klist_waiter *klist_remove_waiters;
+
 static void klist_release(struct kref *kref)
 {
+	struct klist_waiter **pprev, *this;
 	struct klist_node *n = container_of(kref, struct klist_node, n_ref);
 
 	list_del(&n->n_node);
-	complete(&n->n_removed);
+	spin_lock(&klist_remove_lock);
+	pprev = &klist_remove_waiters;
+	while ((this = *pprev)) {
+		if (this->node != n) {
+			pprev = &this->next;
+			continue;
+		}
+
+		this->woken = 1;
+		mb();
+		wake_up_process(this->process);
+		*pprev = this->next;
+	}
+	spin_unlock(&klist_remove_lock);
 	n->n_klist = NULL;
 }
 
@@ -178,8 +201,25 @@ EXPORT_SYMBOL_GPL(klist_del);
  */
 void klist_remove(struct klist_node *n)
 {
+	struct klist_waiter waiter;
+
+	waiter.node = n;
+	waiter.process = current;
+	waiter.woken = 0;
+	spin_lock(&klist_remove_lock);
+	waiter.next = klist_remove_waiters;
+	klist_remove_waiters = &waiter;
+	spin_unlock(&klist_remove_lock);
+
 	klist_del(n);
-	wait_for_completion(&n->n_removed);
+
+	for (;;) {
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		if (waiter.woken)
+			break;
+		schedule();
+	}
+	__set_current_state(TASK_RUNNING);
 }
 EXPORT_SYMBOL_GPL(klist_remove);
 
-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."

Re: [PATCH] Remove completion from struct klist_node

[Greg KH]

On Thu, Oct 02, 2008 at 03:43:08PM -0600, Matthew Wilcox wrote:
> 
> Removing the completion from klist_node reduces its size from 64 bytes
> to 28 on x86-64.  To maintain the semantics of klist_remove(), we add
> a single list of klist nodes which are pending deletion and scan them.
> 
> Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
> 
>  include/linux/klist.h |    2 --
>  lib/klist.c           |   48 ++++++++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 44 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/klist.h b/include/linux/klist.h
> index 06c338e..989a335 100644
> --- a/include/linux/klist.h
> +++ b/include/linux/klist.h
> @@ -13,7 +13,6 @@
>  #define _LINUX_KLIST_H
>  
>  #include <linux/spinlock.h>
> -#include <linux/completion.h>
>  #include <linux/kref.h>
>  #include <linux/list.h>
>  
> @@ -41,7 +40,6 @@ struct klist_node {
>  	struct klist		*n_klist;
>  	struct list_head	n_node;
>  	struct kref		n_ref;
> -	struct completion	n_removed;
>  };
>  
>  extern void klist_add_tail(struct klist_node *n, struct klist *k);
> diff --git a/lib/klist.c b/lib/klist.c
> index cca37f9..2b609ee 100644
> --- a/lib/klist.c
> +++ b/lib/klist.c
> @@ -36,7 +36,7 @@
>  
>  #include <linux/klist.h>
>  #include <linux/module.h>
> -
> +#include <linux/sched.h>
>  
>  /**
>   * klist_init - Initialize a klist structure.
> @@ -77,7 +77,6 @@ static void add_tail(struct klist *k, struct klist_node *n)
>  static void klist_node_init(struct klist *k, struct klist_node *n)
>  {
>  	INIT_LIST_HEAD(&n->n_node);
> -	init_completion(&n->n_removed);
>  	kref_init(&n->n_ref);
>  	n->n_klist = k;
>  	if (k->get)
> @@ -140,12 +139,36 @@ void klist_add_before(struct klist_node *n, struct klist_node *pos)
>  }
>  EXPORT_SYMBOL_GPL(klist_add_before);
>  
> +struct klist_waiter {
> +	struct klist_waiter *next;
> +	struct klist_node *node;
> +	struct task_struct *process;
> +	int woken;
> +};

Why not use the built-in list.h functions here?

Other than that, looks good, thanks.

greg k-h

Re: [PATCH] Remove completion from struct klist_node

[Matthew Wilcox]

On Thu, Oct 02, 2008 at 03:17:45PM -0700, Greg KH wrote:
> > +struct klist_waiter {
> > +	struct klist_waiter *next;
> > +	struct klist_node *node;
> > +	struct task_struct *process;
> > +	int woken;
> > +};
> 
> Why not use the built-in list.h functions here?

I'm somewhat averse to using data structures when they do more than I
need them to.  list_heads are great for when you need to remove an entry
from the middle of a list, but there are no advantages to using a
doubly-linked list here -- we always walk it from the start to the end,
and a singly linked list is fine for this purpose.  Maybe we need a set
of 'slist' macros so we can use singly-linked-lists without thinking
terribly hard, but I'd hate to see this patch get stuck behind
infrastructure improvements.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."

Re: [PATCH] Remove completion from struct klist_node

[Greg KH]

On Fri, Oct 03, 2008 at 08:06:19AM -0600, Matthew Wilcox wrote:
> On Thu, Oct 02, 2008 at 03:17:45PM -0700, Greg KH wrote:
> > > +struct klist_waiter {
> > > +	struct klist_waiter *next;
> > > +	struct klist_node *node;
> > > +	struct task_struct *process;
> > > +	int woken;
> > > +};
> > 
> > Why not use the built-in list.h functions here?
> 
> I'm somewhat averse to using data structures when they do more than I
> need them to.

But part of the point is that if you use them, no one has to audit your
logic to make sure you got it all correct.

> list_heads are great for when you need to remove an entry
> from the middle of a list, but there are no advantages to using a
> doubly-linked list here -- we always walk it from the start to the end,
> and a singly linked list is fine for this purpose.  Maybe we need a set
> of 'slist' macros so we can use singly-linked-lists without thinking
> terribly hard, but I'd hate to see this patch get stuck behind
> infrastructure improvements.

Is size an issue here?  I don't think so and I'd prefer it to be changed
to use the standard list implementation and not roll your own.  You
never know who will cut-and-paste you code these days :)

Care to respin this?

thanks,

greg k-h

Re: [PATCH] Remove completion from struct klist_node

[Matthew Wilcox]

On Fri, Oct 03, 2008 at 01:41:24PM -0700, Greg KH wrote:
> Care to respin this?

Done:

--------

Removing the completion from klist_node reduces its size from 64 bytes
to 28 on x86-64.  To maintain the semantics of klist_remove(), we add
a single list of klist nodes which are pending deletion and scan them.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

diff --git a/include/linux/klist.h b/include/linux/klist.h
index 06c338e..989a335 100644
--- a/include/linux/klist.h
+++ b/include/linux/klist.h
@@ -13,7 +13,6 @@
 #define _LINUX_KLIST_H
 
 #include <linux/spinlock.h>
-#include <linux/completion.h>
 #include <linux/kref.h>
 #include <linux/list.h>
 
@@ -41,7 +40,6 @@ struct klist_node {
 	struct klist		*n_klist;
 	struct list_head	n_node;
 	struct kref		n_ref;
-	struct completion	n_removed;
 };
 
 extern void klist_add_tail(struct klist_node *n, struct klist *k);
diff --git a/lib/klist.c b/lib/klist.c
index cca37f9..50a6b30 100644
--- a/lib/klist.c
+++ b/lib/klist.c
@@ -36,7 +36,7 @@
 
 #include <linux/klist.h>
 #include <linux/module.h>
-
+#include <linux/sched.h>
 
 /**
  * klist_init - Initialize a klist structure.
@@ -77,7 +77,6 @@ static void add_tail(struct klist *k, struct klist_node *n)
 static void klist_node_init(struct klist *k, struct klist_node *n)
 {
 	INIT_LIST_HEAD(&n->n_node);
-	init_completion(&n->n_removed);
 	kref_init(&n->n_ref);
 	n->n_klist = k;
 	if (k->get)
@@ -140,12 +139,33 @@ void klist_add_before(struct klist_node *n, struct klist_node *pos)
 }
 EXPORT_SYMBOL_GPL(klist_add_before);
 
+struct klist_waiter {
+	struct list_head list;
+	struct klist_node *node;
+	struct task_struct *process;
+	int woken;
+};
+
+static DEFINE_SPINLOCK(klist_remove_lock);
+static LIST_HEAD(klist_remove_waiters);
+
 static void klist_release(struct kref *kref)
 {
+	struct klist_waiter *waiter, *tmp;
 	struct klist_node *n = container_of(kref, struct klist_node, n_ref);
 
 	list_del(&n->n_node);
-	complete(&n->n_removed);
+	spin_lock(&klist_remove_lock);
+	list_for_each_entry_safe(waiter, tmp, &klist_remove_waiters, list) {
+		if (waiter->node != n)
+			continue;
+
+		waiter->woken = 1;
+		mb();
+		wake_up_process(waiter->process);
+		list_del(&waiter->list);
+	}
+	spin_unlock(&klist_remove_lock);
 	n->n_klist = NULL;
 }
 
@@ -178,8 +198,24 @@ EXPORT_SYMBOL_GPL(klist_del);
  */
 void klist_remove(struct klist_node *n)
 {
+	struct klist_waiter waiter;
+
+	waiter.node = n;
+	waiter.process = current;
+	waiter.woken = 0;
+	spin_lock(&klist_remove_lock);
+	list_add(&waiter.list, &klist_remove_waiters);
+	spin_unlock(&klist_remove_lock);
+
 	klist_del(n);
-	wait_for_completion(&n->n_removed);
+
+	for (;;) {
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		if (waiter.woken)
+			break;
+		schedule();
+	}
+	__set_current_state(TASK_RUNNING);
 }
 EXPORT_SYMBOL_GPL(klist_remove);
 

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."