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authorVlastimil Babka <vbabka@suse.cz>2016-12-13 03:44:38 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2016-12-13 05:55:08 +0300
commitd5a187daf5856df9b997f9d208e5a7b64006eb2e (patch)
treea9543d74a74fac2bc7a2c5bf378968e92e6fb9b4 /mm
parent46e8a3a08c23d07d0f21fabeed182b671af68c93 (diff)
downloadlinux-d5a187daf5856df9b997f9d208e5a7b64006eb2e.tar.xz
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>
Diffstat (limited to 'mm')
-rw-r--r--mm/rmap.c69
1 files changed, 34 insertions, 35 deletions
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 = find_mergeable_anon_vma(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;
- if (!anon_vma) {
- anon_vma = anon_vma_alloc();
- if (unlikely(!anon_vma))
- goto out_enomem_free_avc;
- allocated = anon_vma;
- }
+ avc = NULL;
+ }
+ spin_unlock(&mm->page_table_lock);
+ anon_vma_unlock_write(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);
- if (unlikely(allocated))
- put_anon_vma(allocated);
- if (unlikely(avc))
- anon_vma_chain_free(avc);
- }
return 0;
out_enomem_free_avc: