mm, rmap: handle anon_vma_prepare() common case inline
anon_vma_prepare() 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 moved away.
[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20161116074005.22768-1-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/rmap.c b/mm/rmap.c
index 1ef3640..91619fd 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: