linux-kernel - [PATCH 2/9] XArray: simplify the calculation of shift

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Message-Id: <20200330123643.17120-3-richard.weiyang@gmail.com>
Date:   Mon, 30 Mar 2020 12:36:36 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     willy@...radead.org
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Wei Yang <richard.weiyang@...il.com>
Subject: [PATCH 2/9] XArray: simplify the calculation of shift

When head is NULL, shift is calculated from max. Currently we use a loop
to detect how many XA_CHUNK_SHIFT is need to cover max.

To achieve this, we can get number of bits max expands and round it up
to XA_CHUNK_SHIFT.

Signed-off-by: Wei Yang <richard.weiyang@...il.com>
---
 lib/xarray.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/lib/xarray.c b/lib/xarray.c
index 1d9fab7db8da..6454cf3f5b4c 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -560,11 +560,7 @@ static int xas_expand(struct xa_state *xas, void *head)
 	unsigned long max = xas_max(xas);
 
 	if (!head) {
-		if (max == 0)
-			return 0;
-		while ((max >> shift) >= XA_CHUNK_SIZE)
-			shift += XA_CHUNK_SHIFT;
-		return shift + XA_CHUNK_SHIFT;
+		return roundup(fls_long(max), XA_CHUNK_SHIFT);
 	} else if (xa_is_node(head)) {
 		node = xa_to_node(head);
 		shift = node->shift + XA_CHUNK_SHIFT;
-- 
2.23.0