From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from p3plsmtps2ded01.prod.phx3.secureserver.net ([208.109.80.58]:48066 "EHLO p3plsmtps2ded01.prod.phx3.secureserver.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S938792AbcKPWYJ (ORCPT ); Wed, 16 Nov 2016 17:24:09 -0500 From: Matthew Wilcox Cc: linux-fsdevel@vger.kernel.org, Matthew Wilcox Subject: [PATCH 25/28] idr: Reduce the number of bits per level from 8 to 6 Date: Wed, 16 Nov 2016 16:17:28 -0800 Message-Id: <1479341856-30320-64-git-send-email-mawilcox@linuxonhyperv.com> In-Reply-To: <1479341856-30320-1-git-send-email-mawilcox@linuxonhyperv.com> References: <1479341856-30320-1-git-send-email-mawilcox@linuxonhyperv.com> To: unlisted-recipients:; (no To-header on input) Sender: linux-fsdevel-owner@vger.kernel.org List-ID: From: Matthew Wilcox In preparation for merging the IDR and radix tree, reduce the fanout at each level from 256 to 64. If this causes a performance problem then a bisect will point to this commit, and we'll have a better idea about what we might do to fix it. Signed-off-by: Matthew Wilcox --- include/linux/idr.h | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/include/linux/idr.h b/include/linux/idr.h index 3639a28..5fd3f6e 100644 --- a/include/linux/idr.h +++ b/include/linux/idr.h @@ -18,12 +18,11 @@ #include /* - * We want shallower trees and thus more bits covered at each layer. 8 - * bits gives us large enough first layer for most use cases and maximum - * tree depth of 4. Each idr_layer is slightly larger than 2k on 64bit and - * 1k on 32bit. + * Using 6 bits at each layer allows us to allocate 7 layers out of each page. + * 8 bits only gave us 3 layers out of every pair of pages, which is less + * efficient except for trees with a largest element between 192-255 inclusive. */ -#define IDR_BITS 8 +#define IDR_BITS 6 #define IDR_SIZE (1 << IDR_BITS) #define IDR_MASK ((1 << IDR_BITS)-1) -- 2.10.2