diff mbox series

[v10,4/5] kprobes: freelist.h removed

Message ID 20231015053251.707442-5-wuqiang.matt@bytedance.com (mailing list archive)
State Superseded
Headers show
Series lib,kprobes: kretprobe scalability improvement | expand

Commit Message

wuqiang.matt Oct. 15, 2023, 5:32 a.m. UTC
This patch will remove freelist.h from kernel source tree, since the
only use cases (kretprobe and rethook) are converted to objpool.

Signed-off-by: wuqiang.matt <wuqiang.matt@bytedance.com>
---
 include/linux/freelist.h | 129 ---------------------------------------
 1 file changed, 129 deletions(-)
 delete mode 100644 include/linux/freelist.h

Comments

Masami Hiramatsu (Google) Oct. 16, 2023, 1:23 p.m. UTC | #1
Hi Peter,

This freelist has been introduced by you, is it OK to remove this because no
other user exists?

Thank you,

On Sun, 15 Oct 2023 13:32:50 +0800
"wuqiang.matt" <wuqiang.matt@bytedance.com> wrote:

> This patch will remove freelist.h from kernel source tree, since the
> only use cases (kretprobe and rethook) are converted to objpool.
> 
> Signed-off-by: wuqiang.matt <wuqiang.matt@bytedance.com>
> ---
>  include/linux/freelist.h | 129 ---------------------------------------
>  1 file changed, 129 deletions(-)
>  delete mode 100644 include/linux/freelist.h
> 
> diff --git a/include/linux/freelist.h b/include/linux/freelist.h
> deleted file mode 100644
> index fc1842b96469..000000000000
> --- a/include/linux/freelist.h
> +++ /dev/null
> @@ -1,129 +0,0 @@
> -/* SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause */
> -#ifndef FREELIST_H
> -#define FREELIST_H
> -
> -#include <linux/atomic.h>
> -
> -/*
> - * Copyright: cameron@moodycamel.com
> - *
> - * A simple CAS-based lock-free free list. Not the fastest thing in the world
> - * under heavy contention, but simple and correct (assuming nodes are never
> - * freed until after the free list is destroyed), and fairly speedy under low
> - * contention.
> - *
> - * Adapted from: https://moodycamel.com/blog/2014/solving-the-aba-problem-for-lock-free-free-lists
> - */
> -
> -struct freelist_node {
> -	atomic_t		refs;
> -	struct freelist_node	*next;
> -};
> -
> -struct freelist_head {
> -	struct freelist_node	*head;
> -};
> -
> -#define REFS_ON_FREELIST 0x80000000
> -#define REFS_MASK	 0x7FFFFFFF
> -
> -static inline void __freelist_add(struct freelist_node *node, struct freelist_head *list)
> -{
> -	/*
> -	 * Since the refcount is zero, and nobody can increase it once it's
> -	 * zero (except us, and we run only one copy of this method per node at
> -	 * a time, i.e. the single thread case), then we know we can safely
> -	 * change the next pointer of the node; however, once the refcount is
> -	 * back above zero, then other threads could increase it (happens under
> -	 * heavy contention, when the refcount goes to zero in between a load
> -	 * and a refcount increment of a node in try_get, then back up to
> -	 * something non-zero, then the refcount increment is done by the other
> -	 * thread) -- so if the CAS to add the node to the actual list fails,
> -	 * decrese the refcount and leave the add operation to the next thread
> -	 * who puts the refcount back to zero (which could be us, hence the
> -	 * loop).
> -	 */
> -	struct freelist_node *head = READ_ONCE(list->head);
> -
> -	for (;;) {
> -		WRITE_ONCE(node->next, head);
> -		atomic_set_release(&node->refs, 1);
> -
> -		if (!try_cmpxchg_release(&list->head, &head, node)) {
> -			/*
> -			 * Hmm, the add failed, but we can only try again when
> -			 * the refcount goes back to zero.
> -			 */
> -			if (atomic_fetch_add_release(REFS_ON_FREELIST - 1, &node->refs) == 1)
> -				continue;
> -		}
> -		return;
> -	}
> -}
> -
> -static inline void freelist_add(struct freelist_node *node, struct freelist_head *list)
> -{
> -	/*
> -	 * We know that the should-be-on-freelist bit is 0 at this point, so
> -	 * it's safe to set it using a fetch_add.
> -	 */
> -	if (!atomic_fetch_add_release(REFS_ON_FREELIST, &node->refs)) {
> -		/*
> -		 * Oh look! We were the last ones referencing this node, and we
> -		 * know we want to add it to the free list, so let's do it!
> -		 */
> -		__freelist_add(node, list);
> -	}
> -}
> -
> -static inline struct freelist_node *freelist_try_get(struct freelist_head *list)
> -{
> -	struct freelist_node *prev, *next, *head = smp_load_acquire(&list->head);
> -	unsigned int refs;
> -
> -	while (head) {
> -		prev = head;
> -		refs = atomic_read(&head->refs);
> -		if ((refs & REFS_MASK) == 0 ||
> -		    !atomic_try_cmpxchg_acquire(&head->refs, &refs, refs+1)) {
> -			head = smp_load_acquire(&list->head);
> -			continue;
> -		}
> -
> -		/*
> -		 * Good, reference count has been incremented (it wasn't at
> -		 * zero), which means we can read the next and not worry about
> -		 * it changing between now and the time we do the CAS.
> -		 */
> -		next = READ_ONCE(head->next);
> -		if (try_cmpxchg_acquire(&list->head, &head, next)) {
> -			/*
> -			 * Yay, got the node. This means it was on the list,
> -			 * which means should-be-on-freelist must be false no
> -			 * matter the refcount (because nobody else knows it's
> -			 * been taken off yet, it can't have been put back on).
> -			 */
> -			WARN_ON_ONCE(atomic_read(&head->refs) & REFS_ON_FREELIST);
> -
> -			/*
> -			 * Decrease refcount twice, once for our ref, and once
> -			 * for the list's ref.
> -			 */
> -			atomic_fetch_add(-2, &head->refs);
> -
> -			return head;
> -		}
> -
> -		/*
> -		 * OK, the head must have changed on us, but we still need to decrement
> -		 * the refcount we increased.
> -		 */
> -		refs = atomic_fetch_add(-1, &prev->refs);
> -		if (refs == REFS_ON_FREELIST + 1)
> -			__freelist_add(prev, list);
> -	}
> -
> -	return NULL;
> -}
> -
> -#endif /* FREELIST_H */
> -- 
> 2.40.1
>
Masami Hiramatsu (Google) Oct. 18, 2023, 3:13 p.m. UTC | #2
Hi,

On Mon, 16 Oct 2023 22:23:14 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> Hi Peter,
> 
> This freelist has been introduced by you, is it OK to remove this because no
> other user exists?

I'll pick this on my probes/for-next branch. If there is any issue reported,
I'll revert it.

Thank you,

> 
> Thank you,
> 
> On Sun, 15 Oct 2023 13:32:50 +0800
> "wuqiang.matt" <wuqiang.matt@bytedance.com> wrote:
> 
> > This patch will remove freelist.h from kernel source tree, since the
> > only use cases (kretprobe and rethook) are converted to objpool.
> > 
> > Signed-off-by: wuqiang.matt <wuqiang.matt@bytedance.com>
> > ---
> >  include/linux/freelist.h | 129 ---------------------------------------
> >  1 file changed, 129 deletions(-)
> >  delete mode 100644 include/linux/freelist.h
> > 
> > diff --git a/include/linux/freelist.h b/include/linux/freelist.h
> > deleted file mode 100644
> > index fc1842b96469..000000000000
> > --- a/include/linux/freelist.h
> > +++ /dev/null
> > @@ -1,129 +0,0 @@
> > -/* SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause */
> > -#ifndef FREELIST_H
> > -#define FREELIST_H
> > -
> > -#include <linux/atomic.h>
> > -
> > -/*
> > - * Copyright: cameron@moodycamel.com
> > - *
> > - * A simple CAS-based lock-free free list. Not the fastest thing in the world
> > - * under heavy contention, but simple and correct (assuming nodes are never
> > - * freed until after the free list is destroyed), and fairly speedy under low
> > - * contention.
> > - *
> > - * Adapted from: https://moodycamel.com/blog/2014/solving-the-aba-problem-for-lock-free-free-lists
> > - */
> > -
> > -struct freelist_node {
> > -	atomic_t		refs;
> > -	struct freelist_node	*next;
> > -};
> > -
> > -struct freelist_head {
> > -	struct freelist_node	*head;
> > -};
> > -
> > -#define REFS_ON_FREELIST 0x80000000
> > -#define REFS_MASK	 0x7FFFFFFF
> > -
> > -static inline void __freelist_add(struct freelist_node *node, struct freelist_head *list)
> > -{
> > -	/*
> > -	 * Since the refcount is zero, and nobody can increase it once it's
> > -	 * zero (except us, and we run only one copy of this method per node at
> > -	 * a time, i.e. the single thread case), then we know we can safely
> > -	 * change the next pointer of the node; however, once the refcount is
> > -	 * back above zero, then other threads could increase it (happens under
> > -	 * heavy contention, when the refcount goes to zero in between a load
> > -	 * and a refcount increment of a node in try_get, then back up to
> > -	 * something non-zero, then the refcount increment is done by the other
> > -	 * thread) -- so if the CAS to add the node to the actual list fails,
> > -	 * decrese the refcount and leave the add operation to the next thread
> > -	 * who puts the refcount back to zero (which could be us, hence the
> > -	 * loop).
> > -	 */
> > -	struct freelist_node *head = READ_ONCE(list->head);
> > -
> > -	for (;;) {
> > -		WRITE_ONCE(node->next, head);
> > -		atomic_set_release(&node->refs, 1);
> > -
> > -		if (!try_cmpxchg_release(&list->head, &head, node)) {
> > -			/*
> > -			 * Hmm, the add failed, but we can only try again when
> > -			 * the refcount goes back to zero.
> > -			 */
> > -			if (atomic_fetch_add_release(REFS_ON_FREELIST - 1, &node->refs) == 1)
> > -				continue;
> > -		}
> > -		return;
> > -	}
> > -}
> > -
> > -static inline void freelist_add(struct freelist_node *node, struct freelist_head *list)
> > -{
> > -	/*
> > -	 * We know that the should-be-on-freelist bit is 0 at this point, so
> > -	 * it's safe to set it using a fetch_add.
> > -	 */
> > -	if (!atomic_fetch_add_release(REFS_ON_FREELIST, &node->refs)) {
> > -		/*
> > -		 * Oh look! We were the last ones referencing this node, and we
> > -		 * know we want to add it to the free list, so let's do it!
> > -		 */
> > -		__freelist_add(node, list);
> > -	}
> > -}
> > -
> > -static inline struct freelist_node *freelist_try_get(struct freelist_head *list)
> > -{
> > -	struct freelist_node *prev, *next, *head = smp_load_acquire(&list->head);
> > -	unsigned int refs;
> > -
> > -	while (head) {
> > -		prev = head;
> > -		refs = atomic_read(&head->refs);
> > -		if ((refs & REFS_MASK) == 0 ||
> > -		    !atomic_try_cmpxchg_acquire(&head->refs, &refs, refs+1)) {
> > -			head = smp_load_acquire(&list->head);
> > -			continue;
> > -		}
> > -
> > -		/*
> > -		 * Good, reference count has been incremented (it wasn't at
> > -		 * zero), which means we can read the next and not worry about
> > -		 * it changing between now and the time we do the CAS.
> > -		 */
> > -		next = READ_ONCE(head->next);
> > -		if (try_cmpxchg_acquire(&list->head, &head, next)) {
> > -			/*
> > -			 * Yay, got the node. This means it was on the list,
> > -			 * which means should-be-on-freelist must be false no
> > -			 * matter the refcount (because nobody else knows it's
> > -			 * been taken off yet, it can't have been put back on).
> > -			 */
> > -			WARN_ON_ONCE(atomic_read(&head->refs) & REFS_ON_FREELIST);
> > -
> > -			/*
> > -			 * Decrease refcount twice, once for our ref, and once
> > -			 * for the list's ref.
> > -			 */
> > -			atomic_fetch_add(-2, &head->refs);
> > -
> > -			return head;
> > -		}
> > -
> > -		/*
> > -		 * OK, the head must have changed on us, but we still need to decrement
> > -		 * the refcount we increased.
> > -		 */
> > -		refs = atomic_fetch_add(-1, &prev->refs);
> > -		if (refs == REFS_ON_FREELIST + 1)
> > -			__freelist_add(prev, list);
> > -	}
> > -
> > -	return NULL;
> > -}
> > -
> > -#endif /* FREELIST_H */
> > -- 
> > 2.40.1
> > 
> 
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@kernel.org>
diff mbox series

Patch

diff --git a/include/linux/freelist.h b/include/linux/freelist.h
deleted file mode 100644
index fc1842b96469..000000000000
--- a/include/linux/freelist.h
+++ /dev/null
@@ -1,129 +0,0 @@ 
-/* SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause */
-#ifndef FREELIST_H
-#define FREELIST_H
-
-#include <linux/atomic.h>
-
-/*
- * Copyright: cameron@moodycamel.com
- *
- * A simple CAS-based lock-free free list. Not the fastest thing in the world
- * under heavy contention, but simple and correct (assuming nodes are never
- * freed until after the free list is destroyed), and fairly speedy under low
- * contention.
- *
- * Adapted from: https://moodycamel.com/blog/2014/solving-the-aba-problem-for-lock-free-free-lists
- */
-
-struct freelist_node {
-	atomic_t		refs;
-	struct freelist_node	*next;
-};
-
-struct freelist_head {
-	struct freelist_node	*head;
-};
-
-#define REFS_ON_FREELIST 0x80000000
-#define REFS_MASK	 0x7FFFFFFF
-
-static inline void __freelist_add(struct freelist_node *node, struct freelist_head *list)
-{
-	/*
-	 * Since the refcount is zero, and nobody can increase it once it's
-	 * zero (except us, and we run only one copy of this method per node at
-	 * a time, i.e. the single thread case), then we know we can safely
-	 * change the next pointer of the node; however, once the refcount is
-	 * back above zero, then other threads could increase it (happens under
-	 * heavy contention, when the refcount goes to zero in between a load
-	 * and a refcount increment of a node in try_get, then back up to
-	 * something non-zero, then the refcount increment is done by the other
-	 * thread) -- so if the CAS to add the node to the actual list fails,
-	 * decrese the refcount and leave the add operation to the next thread
-	 * who puts the refcount back to zero (which could be us, hence the
-	 * loop).
-	 */
-	struct freelist_node *head = READ_ONCE(list->head);
-
-	for (;;) {
-		WRITE_ONCE(node->next, head);
-		atomic_set_release(&node->refs, 1);
-
-		if (!try_cmpxchg_release(&list->head, &head, node)) {
-			/*
-			 * Hmm, the add failed, but we can only try again when
-			 * the refcount goes back to zero.
-			 */
-			if (atomic_fetch_add_release(REFS_ON_FREELIST - 1, &node->refs) == 1)
-				continue;
-		}
-		return;
-	}
-}
-
-static inline void freelist_add(struct freelist_node *node, struct freelist_head *list)
-{
-	/*
-	 * We know that the should-be-on-freelist bit is 0 at this point, so
-	 * it's safe to set it using a fetch_add.
-	 */
-	if (!atomic_fetch_add_release(REFS_ON_FREELIST, &node->refs)) {
-		/*
-		 * Oh look! We were the last ones referencing this node, and we
-		 * know we want to add it to the free list, so let's do it!
-		 */
-		__freelist_add(node, list);
-	}
-}
-
-static inline struct freelist_node *freelist_try_get(struct freelist_head *list)
-{
-	struct freelist_node *prev, *next, *head = smp_load_acquire(&list->head);
-	unsigned int refs;
-
-	while (head) {
-		prev = head;
-		refs = atomic_read(&head->refs);
-		if ((refs & REFS_MASK) == 0 ||
-		    !atomic_try_cmpxchg_acquire(&head->refs, &refs, refs+1)) {
-			head = smp_load_acquire(&list->head);
-			continue;
-		}
-
-		/*
-		 * Good, reference count has been incremented (it wasn't at
-		 * zero), which means we can read the next and not worry about
-		 * it changing between now and the time we do the CAS.
-		 */
-		next = READ_ONCE(head->next);
-		if (try_cmpxchg_acquire(&list->head, &head, next)) {
-			/*
-			 * Yay, got the node. This means it was on the list,
-			 * which means should-be-on-freelist must be false no
-			 * matter the refcount (because nobody else knows it's
-			 * been taken off yet, it can't have been put back on).
-			 */
-			WARN_ON_ONCE(atomic_read(&head->refs) & REFS_ON_FREELIST);
-
-			/*
-			 * Decrease refcount twice, once for our ref, and once
-			 * for the list's ref.
-			 */
-			atomic_fetch_add(-2, &head->refs);
-
-			return head;
-		}
-
-		/*
-		 * OK, the head must have changed on us, but we still need to decrement
-		 * the refcount we increased.
-		 */
-		refs = atomic_fetch_add(-1, &prev->refs);
-		if (refs == REFS_ON_FREELIST + 1)
-			__freelist_add(prev, list);
-	}
-
-	return NULL;
-}
-
-#endif /* FREELIST_H */