From 0ceb13c6f04b8a34e8ba869a5ef17c16e4c355bf Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Tue, 7 Mar 2017 09:04:01 +0100 Subject: [PATCH] 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 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 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 Signed-off-by: Andrew Morton --- mm/filemap.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 1944c631e3e660..e6383acc815640 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2201,12 +2201,12 @@ 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; /* @@ -2255,8 +2255,8 @@ int filemap_fault(struct vm_fault *vmf) * 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; @@ -2322,7 +2322,7 @@ 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(); @@ -2368,8 +2368,8 @@ void filemap_map_pages(struct vm_fault *vmf, 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)