linux-kernel - [PATCH 6/9 V2] idr: avoid ping-pong

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Message-ID: <1397907496-5993-7-git-send-email-laijs@cn.fujitsu.com>
Date:	Sat, 19 Apr 2014 19:38:13 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>, <linux-kernel@...r.kernel.org>
CC:	Lai Jiangshan <laijs@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jean Delvare <jdelvare@...e.de>,
	Monam Agarwal <monamagarwal123@...il.com>,
	Jeff Layton <jlayton@...hat.com>,
	Andreas Gruenbacher <agruen@...bit.com>,
	Stephen Hemminger <stephen@...workplumber.org>
Subject: [PATCH 6/9 V2] idr: avoid ping-pong

The ida callers always calls ida_pre_get() before ida_get_new*().
ida_pre_get() will always do layer allocation, which means the layer removal
in ida_get_new*() is helpless. ida_get_new*() frees and the ida_pre_get() for
the next ida_get_new*() allocates.

It causes an unneeded ping-pong. The aim "Throw away extra resources one by one"
can't be achieved. This speculative layer removal in ida_get_new*() can't
result expected optimization.

So we remove the unneeded layer removal in ida_get_new*().

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
 lib/idr.c |   11 -----------
 1 files changed, 0 insertions(+), 11 deletions(-)

diff --git a/lib/idr.c b/lib/idr.c
index 317fd35..25fe476 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -1001,17 +1001,6 @@ int ida_get_new_above(struct ida *ida, int starting_id, int *p_id)
 
 	*p_id = id;
 
-	/* Each leaf node can handle nearly a thousand slots and the
-	 * whole idea of ida is to have small memory foot print.
-	 * Throw away extra resources one by one after each successful
-	 * allocation.
-	 */
-	if (ida->idr.id_free_cnt || ida->free_bitmap) {
-		struct idr_layer *p = get_from_free_list(&ida->idr);
-		if (p)
-			kmem_cache_free(idr_layer_cache, p);
-	}
-
 	return 0;
 }
 EXPORT_SYMBOL(ida_get_new_above);
-- 
1.7.4.4

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