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Message-ID: <20131106093131.GU28601@twins.programming.kicks-ass.net>
Date: Wed, 6 Nov 2013 10:31:31 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: "Kirill A. Shutemov" <kirill@...temov.name>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH] mm: create a separate slab for page->ptl allocation
On Wed, Nov 06, 2013 at 01:13:11AM +0200, Kirill A. Shutemov wrote:
> I would like to get rid of __ptlock_alloc()/__ptlock_free() too, but I
> don't see a way within C: we need to know sizeof(spinlock_t) on
> preprocessor stage.
>
> We can have a hack on kbuild level: write small helper program to find out
> sizeof(spinlock_t) before start building and turn it into define.
> But it's overkill from my POV. And cross-compilation will be a fun.
Ah, I just remembered, we have such a thing!
---
Subject: mm: Properly separate the bloated ptl from the regular case
Use kernel/bounds.c to convert build-time spinlock_t size into a
preprocessor symbol and apply that to properly separate the page::ptl
situation.
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
---
include/linux/mm.h | 24 +++++++++++++-----------
include/linux/mm_types.h | 9 +++++----
kernel/bounds.c | 2 ++
mm/memory.c | 11 +++++------
4 files changed, 25 insertions(+), 21 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index d0339741b6ce..6ab26704671b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1317,27 +1317,29 @@ static inline pmd_t *pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long a
#endif /* CONFIG_MMU && !__ARCH_HAS_4LEVEL_HACK */
#if USE_SPLIT_PTE_PTLOCKS
-bool __ptlock_alloc(struct page *page);
-void __ptlock_free(struct page *page);
+#if BLOATED_SPINLOCKS
+extern bool ptlock_alloc(struct page *page);
+extern void ptlock_free(struct page *page);
+
+static inline spinlock_t *ptlock_ptr(struct page *page)
+{
+ return page->ptl;
+}
+#else /* BLOATED_SPINLOCKS */
static inline bool ptlock_alloc(struct page *page)
{
- if (sizeof(spinlock_t) > sizeof(page->ptl))
- return __ptlock_alloc(page);
return true;
}
+
static inline void ptlock_free(struct page *page)
{
- if (sizeof(spinlock_t) > sizeof(page->ptl))
- __ptlock_free(page);
}
static inline spinlock_t *ptlock_ptr(struct page *page)
{
- if (sizeof(spinlock_t) > sizeof(page->ptl))
- return (spinlock_t *) page->ptl;
- else
- return (spinlock_t *) &page->ptl;
+ return &page->ptl;
}
+#endif /* BLOATED_SPINLOCKS */
static inline spinlock_t *pte_lockptr(struct mm_struct *mm, pmd_t *pmd)
{
@@ -1354,7 +1356,7 @@ static inline bool ptlock_init(struct page *page)
* slab code uses page->slab_cache and page->first_page (for tail
* pages), which share storage with page->ptl.
*/
- VM_BUG_ON(page->ptl);
+ VM_BUG_ON(*(unsigned long *)&page->ptl);
if (!ptlock_alloc(page))
return false;
spin_lock_init(ptlock_ptr(page));
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 5bee515c4505..f706743b63bb 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -155,10 +155,11 @@ struct page {
* system if PG_buddy is set.
*/
#if USE_SPLIT_PTE_PTLOCKS
- unsigned long ptl; /* It's spinlock_t if it fits to long,
- * otherwise it's pointer to dynamicaly
- * allocated spinlock_t.
- */
+#if BLOATED_SPINLOCKS
+ spinlock_t *ptl;
+#else
+ spinlock_t ptl;
+#endif
#endif
struct kmem_cache *slab_cache; /* SL[AU]B: Pointer to slab */
struct page *first_page; /* Compound tail pages */
diff --git a/kernel/bounds.c b/kernel/bounds.c
index e8ca97b5c386..5982437eca2c 100644
--- a/kernel/bounds.c
+++ b/kernel/bounds.c
@@ -11,6 +11,7 @@
#include <linux/kbuild.h>
#include <linux/page_cgroup.h>
#include <linux/log2.h>
+#include <linux/spinlock.h>
void foo(void)
{
@@ -21,5 +22,6 @@ void foo(void)
#ifdef CONFIG_SMP
DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS));
#endif
+ DEFINE(BLOATED_SPINLOCKS, sizeof(spinlock_t) > sizeof(int));
/* End of constants */
}
diff --git a/mm/memory.c b/mm/memory.c
index 6f7bdee617e2..8356eac27d0a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4271,21 +4271,20 @@ void copy_user_huge_page(struct page *dst, struct page *src,
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */
-#if USE_SPLIT_PTE_PTLOCKS
-bool __ptlock_alloc(struct page *page)
+#if USE_SPLIT_PTE_PTLOCKS && BLOATED_SPINLOCKS
+bool ptlock_alloc(struct page *page)
{
spinlock_t *ptl;
ptl = kmalloc(sizeof(spinlock_t), GFP_KERNEL);
if (!ptl)
return false;
- page->ptl = (unsigned long)ptl;
+ page->ptl = ptl;
return true;
}
-void __ptlock_free(struct page *page)
+void ptlock_free(struct page *page)
{
- if (sizeof(spinlock_t) > sizeof(page->ptl))
- kfree((spinlock_t *)page->ptl);
+ kfree(page->ptl);
}
#endif
--
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