linux-kernel - [PATCH] readahead: use ilog2 instead of a while loop in page_cache_ra

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Date: Mon, 15 Jan 2024 11:25:22 +0100
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: willy@...radead.org,
	akpm@...ux-foundation.org
Cc: linux-mm@...ck.org,
	gost.dev@...sung.com,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Pankaj Raghav <p.raghav@...sung.com>
Subject: [PATCH] readahead: use ilog2 instead of a while loop in page_cache_ra_order()

From: Pankaj Raghav <p.raghav@...sung.com>

A while loop is used to adjust the new_order to be lower than the
ra->size. ilog2 could be used to do the same instead of using a loop.

ilog2 typically resolves to a bit scan reverse instruction. This is
particularly useful when ra->size is smaller than the 2^new_order as it
resolves in one instruction instead of looping to find the new_order.

No functional changes.

Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
---
 mm/readahead.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index c81234fa655a..18b23126eb52 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -500,10 +500,8 @@ void page_cache_ra_order(struct readahead_control *ractl,
 
 	if (new_order < MAX_PAGECACHE_ORDER) {
 		new_order += 2;
-		if (new_order > MAX_PAGECACHE_ORDER)
-			new_order = MAX_PAGECACHE_ORDER;
-		while ((1 << new_order) > ra->size)
-			new_order--;
+		new_order = min_t(unsigned int, MAX_PAGECACHE_ORDER, new_order);
+		new_order = min_t(unsigned int, new_order, ilog2(ra->size));
 	}
 
 	filemap_invalidate_lock_shared(mapping);

base-commit: 8d04a7e2ee3fd6aabb8096b00c64db0d735bc874
-- 
2.43.0