x86, generic: optimize find_next_(zero_)bit for small constant-size bitmaps

This moves an optimization for searching constant-sized small
bitmaps form x86_64-specific to generic code.

On an i386 defconfig (the x86#testing one), the size of vmlinux hardly
changes with this applied. I have observed only four places where this
optimization avoids a call into find_next_bit:

In the functions return_unused_surplus_pages, alloc_fresh_huge_page,
and adjust_pool_surplus, this patch avoids a call for a 1-bit bitmap.
In __next_cpu a call is avoided for a 32-bit bitmap. That's it.

On x86_64, 52 locations are optimized with a minimal increase in
code size:

Current #testing defconfig:
	146 x bsf, 27 x find_next_*bit
   text    data     bss     dec     hex filename
   5392637  846592  724424 6963653  6a41c5 vmlinux

After removing the x86_64 specific optimization for find_next_*bit:
	94 x bsf, 79 x find_next_*bit
   text    data     bss     dec     hex filename
   5392358  846592  724424 6963374  6a40ae vmlinux

After this patch (making the optimization generic):
	146 x bsf, 27 x find_next_*bit
   text    data     bss     dec     hex filename
   5392396  846592  724424 6963412  6a40d4 vmlinux

[ tglx@linutronix.de: build fixes ]

Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 9 insertions, 16 deletions

diff --git a/lib/find_next_bit.c b/lib/find_next_bit.c
index 5820e072b890..ce94c4c92d10 100644
--- a/lib/find_next_bit.c
+++ b/lib/find_next_bit.c
@@ -15,17 +15,12 @@
 #include <asm/byteorder.h>
 
 #define BITOP_WORD(nr)          ((nr) / BITS_PER_LONG)
-#undef find_next_bit
-#undef find_next_zero_bit
-
-/**
- * find_next_bit - find the next set bit in a memory region
- * @addr: The address to base the search on
- * @offset: The bitnumber to start searching at
- * @size: The maximum size to search
+
+/*
+ * Find the next set bit in a memory region.
  */
-unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
-                unsigned long offset)
+unsigned long __find_next_bit(const unsigned long *addr,
+                unsigned long size, unsigned long offset)
 {
         const unsigned long *p = addr + BITOP_WORD(offset);
         unsigned long result = offset & ~(BITS_PER_LONG-1);
@@ -62,15 +57,14 @@ found_first:
 found_middle:
         return result + __ffs(tmp);
 }
-
-EXPORT_SYMBOL(find_next_bit);
+EXPORT_SYMBOL(__find_next_bit);
 
 /*
  * This implementation of find_{first,next}_zero_bit was stolen from
  * Linus' asm-alpha/bitops.h.
  */
-unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
-                unsigned long offset)
+unsigned long __find_next_zero_bit(const unsigned long *addr,
+                unsigned long size, unsigned long offset)
 {
         const unsigned long *p = addr + BITOP_WORD(offset);
         unsigned long result = offset & ~(BITS_PER_LONG-1);
@@ -107,8 +101,7 @@ found_first:
 found_middle:
         return result + ffz(tmp);
 }
-
-EXPORT_SYMBOL(find_next_zero_bit);
+EXPORT_SYMBOL(__find_next_zero_bit);
 
 #ifdef __BIG_ENDIAN