[104/163] mm/mmap: optimize a branch judgment in ksys_mmap_pgoff()
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Message ID 20200807062259.JNE-ENp6G%akpm@linux-foundation.org
State New
Headers show
Series
  • [001/163] mm/memory.c: avoid access flag update TLB flush for retried page fault
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Commit Message

Andrew Morton Aug. 7, 2020, 6:22 a.m. UTC
From: Zhen Lei <thunder.leizhen@huawei.com>
Subject: mm/mmap: optimize a branch judgment in ksys_mmap_pgoff()

Look at the pseudo code below.  It's very clear that, the judgement
"!is_file_hugepages(file)" at 3) is duplicated to the one at 1), we can
use "else if" to avoid it.  And the assignment "retval = -EINVAL" at 2) is
only needed by the branch 3), because "retval" will be overwritten at 4).

No functional change, but it can reduce the code size. Maybe more clearer?
Before:
text    data     bss     dec     hex filename
28733    1590       1   30324    7674 mm/mmap.o

After:
text    data     bss     dec     hex filename
28701    1590       1   30292    7654 mm/mmap.o

====pseudo code====:
	if (!(flags & MAP_ANONYMOUS)) {
		...
1)		if (is_file_hugepages(file))
			len = ALIGN(len, huge_page_size(hstate_file(file)));
2)		retval = -EINVAL;
3)		if (unlikely(flags & MAP_HUGETLB && !is_file_hugepages(file)))
			goto out_fput;
	} else if (flags & MAP_HUGETLB) {
		...
	}
	...

4)	retval = vm_mmap_pgoff(file, addr, len, prot, flags, pgoff);
out_fput:
	...
	return retval;

Link: http://lkml.kernel.org/r/20200705080112.1405-1-thunder.leizhen@huawei.com
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mmap.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Patch
diff mbox series

--- a/mm/mmap.c~mm-mmap-optimize-a-branch-judgment-in-ksys_mmap_pgoff
+++ a/mm/mmap.c
@@ -1562,11 +1562,12 @@  unsigned long ksys_mmap_pgoff(unsigned l
 		file = fget(fd);
 		if (!file)
 			return -EBADF;
-		if (is_file_hugepages(file))
+		if (is_file_hugepages(file)) {
 			len = ALIGN(len, huge_page_size(hstate_file(file)));
-		retval = -EINVAL;
-		if (unlikely(flags & MAP_HUGETLB && !is_file_hugepages(file)))
+		} else if (unlikely(flags & MAP_HUGETLB)) {
+			retval = -EINVAL;
 			goto out_fput;
+		}
 	} else if (flags & MAP_HUGETLB) {
 		struct user_struct *user = NULL;
 		struct hstate *hs;