+ lib-make-bitmap_parselist-thread-safe-and-much-faster.patch added to -mm tree

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/SubmitChecklist when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
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

--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html



[Index of Archives]     [Kernel Archive]     [IETF Annouce]     [DCCP]     [Netdev]     [Networking]     [Security]     [Bugtraq]     [Yosemite]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Linux SCSI]

  Powered by Linux