linux-kernel - [PATCH 04/12] percpu: manage chunks based on contig_bits instead of free

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Message-Id: <20190228021839.55779-5-dennis@kernel.org>
Date:   Wed, 27 Feb 2019 21:18:31 -0500
From:   Dennis Zhou <dennis@...nel.org>
To:     Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>
Cc:     Vlad Buslov <vladbu@...lanox.com>, kernel-team@...com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 04/12] percpu: manage chunks based on contig_bits instead of free_bytes

When a chunk becomes fragmented, it can end up having a large number of
small allocation areas free. The free_bytes sorting of chunks leads to
unnecessary checking of chunks that cannot satisfy the allocation.
Switch to contig_bits sorting to prevent scanning chunks that may not be
able to service the allocation request.

Signed-off-by: Dennis Zhou <dennis@...nel.org>
---
 mm/percpu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index b40112b2fc59..c996bcffbb2a 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -234,7 +234,7 @@ static int pcpu_chunk_slot(const struct pcpu_chunk *chunk)
 	if (chunk->free_bytes < PCPU_MIN_ALLOC_SIZE || chunk->contig_bits == 0)
 		return 0;
 
-	return pcpu_size_to_slot(chunk->free_bytes);
+	return pcpu_size_to_slot(chunk->contig_bits * PCPU_MIN_ALLOC_SIZE);
 }
 
 /* set the pointer to a chunk in a page struct */
-- 
2.17.1