Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754013Ab2FJAoo (ORCPT ); Sat, 9 Jun 2012 20:44:44 -0400 Received: from mail-qc0-f194.google.com ([209.85.216.194]:59672 "EHLO mail-qc0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753169Ab2FJAon (ORCPT ); Sat, 9 Jun 2012 20:44:43 -0400 Date: Sat, 9 Jun 2012 20:44:34 -0400 From: Konrad Rzeszutek Wilk To: Nitin Gupta Cc: Greg KH , Dan Magenheimer , Konrad Rzeszutek Wilk , Seth Jennings , Minchan Kim , linux-mm , linux-kernel Subject: Re: [PATCH v2] zsmalloc documentation Message-ID: <20120610004434.GA24894@localhost.localdomain> References: <1339288874-2743-1-git-send-email-ngupta@vflare.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1339288874-2743-1-git-send-email-ngupta@vflare.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3613 Lines: 89 On Sat, Jun 09, 2012 at 05:41:14PM -0700, Nitin Gupta wrote: > Documentation of various struct page fields > used by zsmalloc. > > Signed-off-by: Nitin Gupta > > Changes for v2: > - Regroup descriptions as suggested by Seth ^^ - Konrad Otherwise: Acked-by: Konrad Rzeszutek Wilk > --- > drivers/staging/zsmalloc/zsmalloc-main.c | 48 ++++++++++++++++++++++++++++++ > 1 file changed, 48 insertions(+) > > diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c > index 4496737..1db76ec 100644 > --- a/drivers/staging/zsmalloc/zsmalloc-main.c > +++ b/drivers/staging/zsmalloc/zsmalloc-main.c > @@ -10,6 +10,54 @@ > * Released under the terms of GNU General Public License Version 2.0 > */ > > + > +/* > + * This allocator is designed for use with zcache and zram. Thus, the > + * allocator is supposed to work well under low memory conditions. In > + * particular, it never attempts higher order page allocation which is > + * very likely to fail under memory pressure. On the other hand, if we > + * just use single (0-order) pages, it would suffer from very high > + * fragmentation -- any object of size PAGE_SIZE/2 or larger would occupy > + * an entire page. This was one of the major issues with its predecessor > + * (xvmalloc). > + * > + * To overcome these issues, zsmalloc allocates a bunch of 0-order pages > + * and links them together using various 'struct page' fields. These linked > + * pages act as a single higher-order page i.e. an object can span 0-order > + * page boundaries. The code refers to these linked pages as a single entity > + * called zspage. > + * > + * Following is how we use various fields and flags of underlying > + * struct page(s) to form a zspage. > + * > + * Usage of struct page fields: > + * page->first_page: points to the first component (0-order) page > + * page->index (union with page->freelist): offset of the first object > + * starting in this page. For the first page, this is > + * always 0, so we use this field (aka freelist) to point > + * to the first free object in zspage. > + * page->lru: links together all component pages (except the first page) > + * of a zspage > + * > + * For _first_ page only: > + * > + * page->private (union with page->first_page): refers to the > + * component page after the first page > + * page->freelist: points to the first free object in zspage. > + * Free objects are linked together using in-place > + * metadata. > + * page->objects: maximum number of objects we can store in this > + * zspage (class->zspage_order * PAGE_SIZE / class->size) > + * page->lru: links together first pages of various zspages. > + * Basically forming list of zspages in a fullness group. > + * page->mapping: class index and fullness group of the zspage > + * > + * Usage of struct page flags: > + * PG_private: identifies the first component page > + * PG_private2: identifies the last component page > + * > + */ > + > #ifdef CONFIG_ZSMALLOC_DEBUG > #define DEBUG > #endif > -- > 1.7.10.2 > > -- > 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/