The patch titled
Subject: lib/bitmap.c: make bitmap_parselist() thread-safe and much faster
has been added to the -mm tree. Its filename is
lib-make-bitmap_parselist-thread-safe-and-much-faster.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/lib-make-bitmap_parselist-thread-safe-and-much-faster.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/lib-make-bitmap_parselist-thread-safe-and-much-faster.patch
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From: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
Subject: lib/bitmap.c: make bitmap_parselist() thread-safe and much faster
Current implementation of bitmap_parselist() uses a static variable to
save local state while setting bits in the bitmap. It is obviously wrong
if we assume execution in multiprocessor environment. Fortunately, it's
possible to rewrite this portion of code to avoid using the static
variable.
It is also possible to set bits in the mask per-range with bitmap_set(),
not per-bit, as it is implemented now, with set_bit(); which is way
faster.
The important side effect of this change is that setting bits in this
function from now is not per-bit atomic and less memory-ordered. This is
because set_bit() guarantees the order of memory accesses, while
bitmap_set() does not. I think that it is the advantage of the new
approach, because the bitmap_parselist() is intended to initialise bit
arrays, and user should protect the whole bitmap during initialisation if
needed. So protecting individual bits looks expensive and useless. Also,
other range-oriented functions in lib/bitmap.c don't worry much about
atomicity.
With all that, setting 2k bits in map with the pattern like 0-2047:128/256
becomes ~50 times faster after applying the patch in my testing
environment (arm64 hosted on qemu).
The second patch of the series adds the test for bitmap_parselist(). It's
not intended to cover all tricky cases, just to make sure that I didn't
screw up during rework.
Link: http://lkml.kernel.org/r/20170807225438.16161-1-ynorov@xxxxxxxxxxxxxxxxxx
Signed-off-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
Cc: Noam Camus <noamca@xxxxxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/bitmap.c | 18 ++++++------------
1 file changed, 6 insertions(+), 12 deletions(-)
diff -puN lib/bitmap.c~lib-make-bitmap_parselist-thread-safe-and-much-faster lib/bitmap.c
--- a/lib/bitmap.c~lib-make-bitmap_parselist-thread-safe-and-much-faster
+++ a/lib/bitmap.c
@@ -513,7 +513,7 @@ static int __bitmap_parselist(const char
int nmaskbits)
{
unsigned int a, b, old_a, old_b;
- unsigned int group_size, used_size;
+ unsigned int group_size, used_size, off;
int c, old_c, totaldigits, ndigits;
const char __user __force *ubuf = (const char __user __force *)buf;
int at_start, in_range, in_partial_range;
@@ -599,6 +599,8 @@ static int __bitmap_parselist(const char
a = old_a;
b = old_b;
old_a = old_b = 0;
+ } else {
+ used_size = group_size = b - a + 1;
}
/* if no digit is after '-', it's wrong*/
if (at_start && in_range)
@@ -608,17 +610,9 @@ static int __bitmap_parselist(const char
if (b >= nmaskbits)
return -ERANGE;
while (a <= b) {
- if (in_partial_range) {
- static int pos_in_group = 1;
-
- if (pos_in_group <= used_size)
- set_bit(a, maskp);
-
- if (a == b || ++pos_in_group > group_size)
- pos_in_group = 1;
- } else
- set_bit(a, maskp);
- a++;
+ off = min(b - a + 1, used_size);
+ bitmap_set(maskp, a, off);
+ a += group_size;
}
} while (buflen && c == ',');
return 0;
_
Patches currently in -mm which might be from ynorov@xxxxxxxxxxxxxxxxxx are
lib-make-bitmap_parselist-thread-safe-and-much-faster.patch
lib-add-test-for-bitmap_parselist.patch
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