From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f169.google.com (mail-pf0-f169.google.com [209.85.192.169]) by kanga.kvack.org (Postfix) with ESMTP id AFDF56B0009 for ; Fri, 19 Feb 2016 00:36:59 -0500 (EST) Received: by mail-pf0-f169.google.com with SMTP id c10so46304968pfc.2 for ; Thu, 18 Feb 2016 21:36:59 -0800 (PST) Received: from mail-pa0-x234.google.com (mail-pa0-x234.google.com. [2607:f8b0:400e:c03::234]) by mx.google.com with ESMTPS id 68si14222353pfj.77.2016.02.18.21.36.58 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 18 Feb 2016 21:36:58 -0800 (PST) Received: by mail-pa0-x234.google.com with SMTP id fl4so44281908pad.0 for ; Thu, 18 Feb 2016 21:36:58 -0800 (PST) Date: Fri, 19 Feb 2016 14:38:14 +0900 From: 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> Sender: owner-linux-mm@kvack.org List-ID: To: Sergey Senozhatsky Cc: Joonsoo Kim , Andrew Morton , Minchan Kim , Linux Memory Management List , LKML , Sergey Senozhatsky 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 -- 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