linux-kernel - [PATCH v2 7/8] btrfs/free-space-cache.c: Apply find_last_zero

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Message-ID: <20201206065004.GA6321@ubuntu>
Date:   Sun, 6 Dec 2020 15:50:04 +0900
From:   Levi Yun <ppbuk5246@...il.com>
To:     akpm@...ux-foundation.org, yury.norov@...il.com,
        andriy.shevchenko@...ux.intel.com,
        richard.weiyang@...ux.alibaba.com, christian.brauner@...ntu.com,
        arnd@...db.de, jpoimboe@...hat.com, changbin.du@...el.com,
        rdunlap@...radead.org, masahiroy@...nel.org,
        gregkh@...uxfoundation.org, peterz@...radead.org,
        peter.enderborg@...y.com, krzk@...nel.org,
        brendanhiggins@...gle.com, keescook@...omium.org,
        broonie@...nel.org, matti.vaittinen@...rohmeurope.com,
        mhiramat@...nel.org, jpa@....mail.kapsi.fi, nivedita@...m.mit.edu,
        glider@...gle.com, orson.zhai@...soc.com,
        takahiro.akashi@...aro.org, clm@...com, josef@...icpanda.com,
        dsterba@...e.com, dushistov@...l.ru
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-btrfs@...r.kernel.org
Subject: [PATCH v2 7/8] btrfs/free-space-cache.c: Apply find_last_zero_bit

In steal_from_bitmap_to_front function, it finds last_zero_bit from i
using for_each_clear_bit.
But this makes some overhead that it starts from the 0 bit.
By adding find_last_zero_bit, I try to remove this overhead and
improve readibility.

Signed-off-by: Levi Yun <ppbuk5246@...il.com>
---
 fs/btrfs/free-space-cache.c | 22 ++++++++--------------
 1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index af0013d3df63..6d393c834fdd 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -2372,7 +2372,6 @@ static bool steal_from_bitmap_to_front(struct btrfs_free_space_ctl *ctl,
 	u64 bitmap_offset;
 	unsigned long i;
 	unsigned long j;
-	unsigned long prev_j;
 	u64 bytes;
 
 	bitmap_offset = offset_to_bitmap(ctl, info->offset);
@@ -2388,20 +2387,15 @@ static bool steal_from_bitmap_to_front(struct btrfs_free_space_ctl *ctl,
 		return false;
 
 	i = offset_to_bit(bitmap->offset, ctl->unit, info->offset) - 1;
-	j = 0;
-	prev_j = (unsigned long)-1;
-	for_each_clear_bit_from(j, bitmap->bitmap, BITS_PER_BITMAP) {
-		if (j > i)
-			break;
-		prev_j = j;
-	}
-	if (prev_j == i)
-		return false;
+	j = find_last_zero_bit(bitmap->bitmap, i);
 
-	if (prev_j == (unsigned long)-1)
-		bytes = (i + 1) * ctl->unit;
-	else
-		bytes = (i - prev_j) * ctl->unit;
+	if (j == i) {
+		if (!test_bit(i, bitmap->bitmap))
+			return false;
+		else
+			bytes = (i + 1) * ctl->unit;
+	} else
+		bytes = (i - j) * ctl->unit;
 
 	info->offset -= bytes;
 	info->bytes += bytes;
-- 
2.27.0