From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1424652AbcBREkm (ORCPT ); Wed, 17 Feb 2016 23:40:42 -0500 Received: from mail-pa0-f45.google.com ([209.85.220.45]:33693 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1424254AbcBREkl (ORCPT ); Wed, 17 Feb 2016 23:40:41 -0500 Date: Thu, 18 Feb 2016 13:41:56 +0900 From: Sergey Senozhatsky To: Sergey Senozhatsky Cc: Andrew Morton , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: Re: [RFC PATCH 3/3] mm/zsmalloc: change ZS_MAX_PAGES_PER_ZSPAGE Message-ID: <20160218044156.GA10776@swordfish> References: <1455764556-13979-1-git-send-email-sergey.senozhatsky@gmail.com> <1455764556-13979-4-git-send-email-sergey.senozhatsky@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1455764556-13979-4-git-send-email-sergey.senozhatsky@gmail.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (02/18/16 12:02), Sergey Senozhatsky wrote: [..] > --- > mm/zsmalloc.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > index 61b1b35..0c9f117 100644 > --- a/mm/zsmalloc.c > +++ b/mm/zsmalloc.c > @@ -74,11 +74,10 @@ > #define ZS_ALIGN 8 > > /* > - * A single 'zspage' is composed of up to 2^N discontiguous 0-order (single) > - * pages. ZS_MAX_ZSPAGE_ORDER defines upper limit on N. > + * A single 'zspage' is composed of up ZS_MAX_PAGES_PER_ZSPAGE discontiguous > + * 0-order (single) pages. > */ > -#define ZS_MAX_ZSPAGE_ORDER 2 > -#define ZS_MAX_PAGES_PER_ZSPAGE (_AC(1, UL) << ZS_MAX_ZSPAGE_ORDER) > +#define ZS_MAX_PAGES_PER_ZSPAGE 6 > > #define ZS_HANDLE_SIZE (sizeof(unsigned long)) > I think we better switch to different logic here -- specify how many ->huge classes we want to have, and let zsmalloc to calculate ZS_MAX_PAGES_PER_ZSPAGE. For example, if we want to have 20 ->huge classes, the 'smallest' (or the last) non-huge class will have CLASS_SIZE * SIZE_CLASS_DELTA of spare (wasted) space, so PAGE_SIZE / (CLASS_SIZE * SIZE_CLASS_DELTA) will give us the number of pages we need to form into a zspage to make it the last huge class. setting ZS_MIN_HUGE_CLASSES_NUM to 32 gives us (on x86_64, PAGE_SHIFT 12) ->huge class size range of [3648, 4096]. so all objects smaller than 3648 will not waste an entire zspage (and order-0 page), but will share the page with another objects of that size. something like this: --- diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 0c9f117..d5252d1 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -73,12 +73,6 @@ */ #define ZS_ALIGN 8 -/* - * A single 'zspage' is composed of up ZS_MAX_PAGES_PER_ZSPAGE discontiguous - * 0-order (single) pages. - */ -#define ZS_MAX_PAGES_PER_ZSPAGE 6 - #define ZS_HANDLE_SIZE (sizeof(unsigned long)) /* @@ -149,6 +143,21 @@ #define ZS_SIZE_CLASS_DELTA (PAGE_SIZE >> 8) /* + * We want to have at least this number of ->huge classes. + */ +#define ZS_MIN_HUGE_CLASSES_NUM 32 +/* + * A single 'zspage' is composed of up ZS_MAX_PAGES_PER_ZSPAGE discontiguous + * 0-order (single) pages. + * + * The smallest huge class will have CLASS_SIZE * SIZE_CLASS_DELTA of + * wasted space, calculate how many pages we need to fit a CLASS_SIZE + * object there and, thus, to save a additional zspage. + */ +#define ZS_MAX_PAGES_PER_ZSPAGE \ + (PAGE_SIZE / (ZS_MIN_HUGE_CLASSES_NUM * ZS_SIZE_CLASS_DELTA)) + +/* * We do not maintain any list for completely empty or full pages */ enum fullness_group {