From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757689AbcBSFhA (ORCPT ); Fri, 19 Feb 2016 00:37:00 -0500 Received: from mail-pa0-f44.google.com ([209.85.220.44]:36041 "EHLO mail-pa0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757629AbcBSFg7 (ORCPT ); Fri, 19 Feb 2016 00:36:59 -0500 Date: Fri, 19 Feb 2016 14:38:14 +0900 From: Sergey Senozhatsky To: Sergey Senozhatsky Cc: Joonsoo Kim , Andrew Morton , Minchan Kim , Linux Memory Management List , LKML , Sergey Senozhatsky Subject: Re: [RFC PATCH 3/3] mm/zsmalloc: change ZS_MAX_PAGES_PER_ZSPAGE Message-ID: <20160219053814.GB16230@swordfish> References: <1455764556-13979-1-git-send-email-sergey.senozhatsky@gmail.com> <1455764556-13979-4-git-send-email-sergey.senozhatsky@gmail.com> <20160218095536.GA503@swordfish> <20160218101909.GB503@swordfish> <20160219041601.GA820@swordfish> <20160219044604.GA16230@swordfish> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160219044604.GA16230@swordfish> 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 (02/19/16 13:46), Sergey Senozhatsky wrote: > On (02/19/16 13:16), Sergey Senozhatsky wrote: > > ok, this sets us on a "do we need 32 and 48 bytes classes at all" track? > > > > seems that lz4 defines a minimum length to be at least > > 61 #define COPYLENGTH 8 > 67 #define MINMATCH 4 > 70 #define MFLIMIT (COPYLENGTH + MINMATCH) > 71 #define MINLENGTH (MFLIMIT + 1) > > bytes. hm, on a second look, zsmalloc defines the following macros: #define ZS_MAX_ZSPAGE_ORDER 2 #define ZS_MAX_PAGES_PER_ZSPAGE (_AC(1, UL) << ZS_MAX_ZSPAGE_ORDER) #ifndef MAX_PHYSMEM_BITS #ifdef CONFIG_HIGHMEM64G #define MAX_PHYSMEM_BITS 36 #else /* !CONFIG_HIGHMEM64G */ /* * If this definition of MAX_PHYSMEM_BITS is used, OBJ_INDEX_BITS will just * be PAGE_SHIFT */ #define MAX_PHYSMEM_BITS BITS_PER_LONG #endif #endif #define _PFN_BITS (MAX_PHYSMEM_BITS - PAGE_SHIFT) #define OBJ_ALLOCATED_TAG 1 #define OBJ_TAG_BITS 1 #define OBJ_INDEX_BITS (BITS_PER_LONG - _PFN_BITS - OBJ_TAG_BITS) #define OBJ_INDEX_MASK ((_AC(1, UL) << OBJ_INDEX_BITS) - 1) #define ZS_MIN_ALLOC_SIZE \ MAX(32, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OBJ_INDEX_BITS)) so let's do some calculations, hopefuly I'm not mistaken anywhere. with ZS_MAX_ZSPAGE_ORDER 4 -- on 32 bit system, PAGE_SHIFT 12 ZS_MAX_PAGES_PER_ZSPAGE 1 << 4 16 OBJ_INDEX_BITS (32 - (32 - 12) - 1) 11 OBJ_INDEX_MASK ((1 << (32 - (32 - 12) - 1)) - 1) 2047 ZS_MIN_ALLOC_SIZE MAX(32, ((1 << 4) << 12 >> (32 - (32 - 12) - 1))) 32 -- on 64 bit system, PAGE_SHIFT 12 ZS_MAX_PAGES_PER_ZSPAGE 1 << 4 16 OBJ_INDEX_BITS (64 - (64 - 12) - 1) 11 OBJ_INDEX_MASK ((1 << (64 - (64 - 12) - 1)) - 1) 2047 ZS_MIN_ALLOC_SIZE MAX(32, ((1 << 4) << 12 >> (64 - (64 - 12) - 1))) 32 -- on 64 bit system, PAGE_SHIFT 14 ZS_MAX_PAGES_PER_ZSPAGE 1 << 4 16 OBJ_INDEX_BITS (64 - (64 - 14) - 1) 13 OBJ_INDEX_MASK ((1 << (64 - (64 - 14) - 1)) - 1) 8191 ZS_MIN_ALLOC_SIZE MAX(32, ((1 << 4) << 14 >> (64 - (64 - 14) - 1))) 32 -- on 64 bit system, PAGE_SHIFT 16 ZS_MAX_PAGES_PER_ZSPAGE 1 << 4 16 OBJ_INDEX_BITS (64 - (64 - 16) - 1) 15 OBJ_INDEX_MASK ((1 << (64 - (64 - 16) - 1)) - 1) 32767 ZS_MIN_ALLOC_SIZE MAX(32, ((1 << 4) << 16 >> (64 - (64 - 14) - 1))) 128 << bad so, isn't it enough OBJ_INDEX_BITS bits to even keep 32 bytes class around? we probably would prefer to lower ZS_MAX_ZSPAGE_ORDER on PAGE_SHIFT 16 systems. for example to ZS_MAX_PAGES_PER_ZSPAGE 1 << 3, or 1 << 2. and of course LPAE/PAE enabled systems -- leave ZS_MAX_ZSPAGE_ORDER 2 there. ZS_MAX_PAGES_PER_ZSPAGE 1 << 4 gives us # cat /sys/kernel/debug/zsmalloc/zram0/classes class size huge almost_full almost_empty obj_allocated obj_used pages_used pages_per_zspage 0 32 0 0 0 0 0 1 ... 238 3840 0 0 0 0 0 15 254 4096 Y 0 0 0 0 0 1 so starting from 3840+ we have huge classes, the rest are 'normal' classes and will save memory there in theory. -ss