linux-kernel - Re: [PATCH -next] mm/vmacache: inline vmacache_valid

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Date:	Thu, 8 Oct 2015 15:21:15 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Davidlohr Bueso <dave@...olabs.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH -next] mm/vmacache: inline vmacache_valid_mm()

On (10/07/15 21:17), Davidlohr Bueso wrote:
> This function incurs in very hot paths and merely
> does a few loads for validity check. Lets inline it,
> such that we can save the function call overhead.
> 
> Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
> ---
>  mm/vmacache.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmacache.c b/mm/vmacache.c
> index b6e3662..fd09dc9 100644
> --- a/mm/vmacache.c
> +++ b/mm/vmacache.c
> @@ -52,7 +52,7 @@ void vmacache_flush_all(struct mm_struct *mm)
>   * Also handle the case where a kernel thread has adopted this mm via use_mm().
>   * That kernel thread's vmacache is not applicable to this mm.
>   */
> -static bool vmacache_valid_mm(struct mm_struct *mm)
> +static inline bool vmacache_valid_mm(struct mm_struct *mm)
>  {
>  	return current->mm == mm && !(current->flags & PF_KTHREAD);
>  }

Seems to be inlined anyway. do you want to inline vmacache_update()?
It looks simple enough (vmacache_valid_mm() is inlined):

void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
{
	if (vmacache_valid_mm(newvma->vm_mm))
		current->vmacache[VMACACHE_HASH(addr)] = newvma;
}


After moving vmacache_update() and vmacache_valid_mm() to include/linux/vmacache.h
(both `static inline')


./scripts/bloat-o-meter vmlinux.o.old vmlinux.o
add/remove: 0/1 grow/shrink: 1/0 up/down: 22/-54 (-32)
function                                     old     new   delta
find_vma                                      97     119     +22
vmacache_update                               54       -     -54


Something like this, perhaps?

---

 include/linux/vmacache.h | 21 ++++++++++++++++++++-
 mm/vmacache.c            | 20 --------------------
 2 files changed, 20 insertions(+), 21 deletions(-)

diff --git a/include/linux/vmacache.h b/include/linux/vmacache.h
index c3fa0fd4..0ec750b 100644
--- a/include/linux/vmacache.h
+++ b/include/linux/vmacache.h
@@ -15,8 +15,27 @@ static inline void vmacache_flush(struct task_struct *tsk)
 	memset(tsk->vmacache, 0, sizeof(tsk->vmacache));
 }
 
+/*
+ * This task may be accessing a foreign mm via (for example)
+ * get_user_pages()->find_vma().  The vmacache is task-local and this
+ * task's vmacache pertains to a different mm (ie, its own).  There is
+ * nothing we can do here.
+ *
+ * Also handle the case where a kernel thread has adopted this mm via use_mm().
+ * That kernel thread's vmacache is not applicable to this mm.
+ */
+static bool vmacache_valid_mm(struct mm_struct *mm)
+{
+	return current->mm == mm && !(current->flags & PF_KTHREAD);
+}
+
+static inline void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
+{
+	if (vmacache_valid_mm(newvma->vm_mm))
+		current->vmacache[VMACACHE_HASH(addr)] = newvma;
+}
+
 extern void vmacache_flush_all(struct mm_struct *mm);
-extern void vmacache_update(unsigned long addr, struct vm_area_struct *newvma);
 extern struct vm_area_struct *vmacache_find(struct mm_struct *mm,
 						    unsigned long addr);
 
diff --git a/mm/vmacache.c b/mm/vmacache.c
index b6e3662..14fec21 100644
--- a/mm/vmacache.c
+++ b/mm/vmacache.c
@@ -43,26 +43,6 @@ void vmacache_flush_all(struct mm_struct *mm)
 	rcu_read_unlock();
 }
 
-/*
- * This task may be accessing a foreign mm via (for example)
- * get_user_pages()->find_vma().  The vmacache is task-local and this
- * task's vmacache pertains to a different mm (ie, its own).  There is
- * nothing we can do here.
- *
- * Also handle the case where a kernel thread has adopted this mm via use_mm().
- * That kernel thread's vmacache is not applicable to this mm.
- */
-static bool vmacache_valid_mm(struct mm_struct *mm)
-{
-	return current->mm == mm && !(current->flags & PF_KTHREAD);
-}
-
-void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
-{
-	if (vmacache_valid_mm(newvma->vm_mm))
-		current->vmacache[VMACACHE_HASH(addr)] = newvma;
-}
-
 static bool vmacache_valid(struct mm_struct *mm)
 {
 	struct task_struct *curr;

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