diff options
| author | Matthew Wilcox <mawilcox@microsoft.com> | 2017-05-03 14:53:29 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-05-03 15:52:09 -0700 |
| commit | 9ab2594febb468964a4c00f8023ec22073ca8716 (patch) | |
| tree | cc9ab63967d6a6d339ea3359c5161df252fc5ccc | |
| parent | eb52da3f48f5b1ddceb7e8d4725b6c88204aa2c4 (diff) | |
mm: tighten up the fault path a little
The round_up() macro generates a couple of unnecessary instructions
in this usage:
48cd: 49 8b 47 50 mov 0x50(%r15),%rax
48d1: 48 83 e8 01 sub $0x1,%rax
48d5: 48 0d ff 0f 00 00 or $0xfff,%rax
48db: 48 83 c0 01 add $0x1,%rax
48df: 48 c1 f8 0c sar $0xc,%rax
48e3: 48 39 c3 cmp %rax,%rbx
48e6: 72 2e jb 4916 <filemap_fault+0x96>
If we change round_up() to ((x) + __round_mask(x, y)) & ~__round_mask(x, y)
then GCC can see through it and remove the mask (because that would be
dead code given the subsequent shift):
48cd: 49 8b 47 50 mov 0x50(%r15),%rax
48d1: 48 05 ff 0f 00 00 add $0xfff,%rax
48d7: 48 c1 e8 0c shr $0xc,%rax
48db: 48 39 c3 cmp %rax,%rbx
48de: 72 2e jb 490e <filemap_fault+0x8e>
But that's problematic because we'd evaluate 'y' twice. Converting
round_up into an inline function prevents it from being used in other
definitions. The easiest thing to do is just change these three usages
of round_up to use DIV_ROUND_UP. Also add an unlikely() because GCC's
heuristic is wrong in this case.
Link: http://lkml.kernel.org/r/20170207192812.5281-1-willy@infradead.org
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | mm/filemap.c | 16 |
1 files changed, 8 insertions, 8 deletions
diff --git a/mm/filemap.c b/mm/filemap.c index dc59c5f35b37..7f425f18c158 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2204,12 +2204,12 @@ int filemap_fault(struct vm_fault *vmf) struct file_ra_state *ra = &file->f_ra; struct inode *inode = mapping->host; pgoff_t offset = vmf->pgoff; + pgoff_t max_off; struct page *page; - loff_t size; int ret = 0; - size = round_up(i_size_read(inode), PAGE_SIZE); - if (offset >= size >> PAGE_SHIFT) + max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); + if (unlikely(offset >= max_off)) return VM_FAULT_SIGBUS; /* @@ -2258,8 +2258,8 @@ retry_find: * Found the page and have a reference on it. * We must recheck i_size under page lock. */ - size = round_up(i_size_read(inode), PAGE_SIZE); - if (unlikely(offset >= size >> PAGE_SHIFT)) { + max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); + if (unlikely(offset >= max_off)) { unlock_page(page); put_page(page); return VM_FAULT_SIGBUS; @@ -2325,7 +2325,7 @@ void filemap_map_pages(struct vm_fault *vmf, struct file *file = vmf->vma->vm_file; struct address_space *mapping = file->f_mapping; pgoff_t last_pgoff = start_pgoff; - loff_t size; + unsigned long max_idx; struct page *head, *page; rcu_read_lock(); @@ -2371,8 +2371,8 @@ repeat: if (page->mapping != mapping || !PageUptodate(page)) goto unlock; - size = round_up(i_size_read(mapping->host), PAGE_SIZE); - if (page->index >= size >> PAGE_SHIFT) + max_idx = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE); + if (page->index >= max_idx) goto unlock; if (file->f_ra.mmap_miss > 0) |