From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Matthew Wilcox To: linux-kernel@vger.kernel.org, Andrew Morton , Konstantin Khlebnikov , Ross Zwisler Cc: linux-fsdevel@vger.kernel.org, Matthew Wilcox , linux-mm@kvack.org, "Kirill A . Shutemov" Subject: [PATCH 26/29] idr: Reduce the number of bits per level from 8 to 6 Date: Wed, 16 Nov 2016 16:17:30 -0800 Message-Id: <1479341856-30320-66-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> Sender: owner-linux-mm@kvack.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 1eb755f..3c01b89 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org