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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>
This commit is contained in:
Vlastimil Babka 2016-12-12 16:44:38 -08:00 committed by Linus Torvalds
parent 46e8a3a08c
commit d5a187daf5
2 changed files with 45 additions and 38 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
include/linux/rmap.h
View File

@ -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)
{

15
mm/rmap.c
View File

@ -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
@ -167,15 +168,13 @@ 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)
@ -208,7 +207,7 @@ int anon_vma_prepare(struct vm_area_struct *vma)
put_anon_vma(allocated);
if (unlikely(avc))
anon_vma_chain_free(avc);
}
return 0;
out_enomem_free_avc: