The anon_vma_prepare() function is mostly a large "if (unlikely(...))" block,
as the expected common case is that an anon_vma already exists. We could turn
the condition around and return 0, but it also makes sense to do it inline and
avoid a call for the common case.
Bloat-o-meter naturally shows that inlining the check has some code size costs:
add/remove: 1/1 grow/shrink: 4/0 up/down: 475/-373 (102)
function old new delta
__anon_vma_prepare - 359 +359
handle_mm_fault 2744 2796 +52
hugetlb_cow 1146 1170 +24
hugetlb_fault 2123 2145 +22
wp_page_copy 1469 1487 +18
anon_vma_prepare 373 - -373
Checking the asm however confirms that the hot paths now avoid a call, which
is now moved away.
Signed-off-by: Vlastimil Babka <vba...@suse.cz>
Cc: "Kirill A. Shutemov" <kirill.shute...@linux.intel.com>
Cc: Johannes Weiner <han...@cmpxchg.org>
Cc: Konstantin Khlebnikov <koc...@gmail.com>
Cc: Rik van Riel <r...@redhat.com>
---
include/linux/rmap.h | 10 ++++++-
mm/rmap.c | 73 ++++++++++++++++++++++++++--------------------------
2 files changed, 45 insertions(+), 38 deletions(-)
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index b46bb5620a76..850da50c574e 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -137,11 +137,19 @@ static inline void anon_vma_unlock_read(struct anon_vma
*anon_vma)
* anon_vma helper functions.
*/
void anon_vma_init(void); /* create anon_vma_cachep */
-int anon_vma_prepare(struct vm_area_struct *);
+int __anon_vma_prepare(struct vm_area_struct *);
void unlink_anon_vmas(struct vm_area_struct *);
int anon_vma_clone(struct vm_area_struct *, struct vm_area_struct *);
int anon_vma_fork(struct vm_area_struct *, struct vm_area_struct *);
+static inline int anon_vma_prepare(struct vm_area_struct * vma)
+{
+ if (likely(vma->anon_vma))
+ return 0;
+
+ return __anon_vma_prepare(vma);
+}
+
static inline void anon_vma_merge(struct vm_area_struct *vma,
struct vm_area_struct *next)
{
diff --git a/mm/rmap.c b/mm/rmap.c
index 1ef36404e7b2..91619fd70939 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -141,14 +141,15 @@ static void anon_vma_chain_link(struct vm_area_struct
*vma,
}
/**
- * anon_vma_prepare - attach an anon_vma to a memory region
+ * __anon_vma_prepare - attach an anon_vma to a memory region
* @vma: the memory region in question
*
* This makes sure the memory mapping described by 'vma' has
* an 'anon_vma' attached to it, so that we can associate the
* anonymous pages mapped into it with that anon_vma.
*
- * The common case will be that we already have one, but if
+ * The common case will be that we already have one, which
+ * is handled inline by anon_vma_prepare(). But if
* not we either need to find an adjacent mapping that we
* can re-use the anon_vma from (very common when the only
* reason for splitting a vma has been mprotect()), or we
@@ -167,48 +168,46 @@ static void anon_vma_chain_link(struct vm_area_struct
*vma,
*
* This must be called with the mmap_sem held for reading.
*/
-int anon_vma_prepare(struct vm_area_struct *vma)
+int __anon_vma_prepare(struct vm_area_struct *vma)
{
- struct anon_vma *anon_vma = vma->anon_vma;
+ struct mm_struct *mm = vma->vm_mm;
+ struct anon_vma *anon_vma, *allocated;
struct anon_vma_chain *avc;
might_sleep();
- if (unlikely(!anon_vma)) {
- struct mm_struct *mm = vma->vm_mm;
- struct anon_vma *allocated;
- avc = anon_vma_chain_alloc(GFP_KERNEL);
- if (!avc)
- goto out_enomem;
+ avc = anon_vma_chain_alloc(GFP_KERNEL);
+ if (!avc)
+ goto out_enomem;
- anon_vma = find_mergeable_anon_vma(vma);
- allocated = NULL;
- if (!anon_vma) {
- anon_vma = anon_vma_alloc();
- if (unlikely(!anon_vma))
- goto out_enomem_free_avc;
- allocated = anon_vma;
- }
-
- anon_vma_lock_write(anon_vma);
- /* page_table_lock to protect against threads */
- spin_lock(&mm->page_table_lock);
- if (likely(!vma->anon_vma)) {
- vma->anon_vma = anon_vma;
- anon_vma_chain_link(vma, avc, anon_vma);
- /* vma reference or self-parent link for new root */
- anon_vma->degree++;
- allocated = NULL;
- avc = NULL;
- }
- spin_unlock(&mm->page_table_lock);
- anon_vma_unlock_write(anon_vma);
-
- if (unlikely(allocated))
- put_anon_vma(allocated);
- if (unlikely(avc))
- anon_vma_chain_free(avc);
+ anon_vma = find_mergeable_anon_vma(vma);
+ allocated = NULL;
+ if (!anon_vma) {
+ anon_vma = anon_vma_alloc();
+ if (unlikely(!anon_vma))
+ goto out_enomem_free_avc;
+ allocated = anon_vma;
}
+
+ anon_vma_lock_write(anon_vma);
+ /* page_table_lock to protect against threads */
+ spin_lock(&mm->page_table_lock);
+ if (likely(!vma->anon_vma)) {
+ vma->anon_vma = anon_vma;
+ anon_vma_chain_link(vma, avc, anon_vma);
+ /* vma reference or self-parent link for new root */
+ anon_vma->degree++;
+ allocated = NULL;
+ avc = NULL;
+ }
+ spin_unlock(&mm->page_table_lock);
+ anon_vma_unlock_write(anon_vma);
+
+ if (unlikely(allocated))
+ put_anon_vma(allocated);
+ if (unlikely(avc))
+ anon_vma_chain_free(avc);
+
return 0;
out_enomem_free_avc:
--
2.10.2
