From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f199.google.com (mail-io0-f199.google.com [209.85.223.199]) by kanga.kvack.org (Postfix) with ESMTP id A87C36B007E for ; Tue, 19 Apr 2016 03:41:42 -0400 (EDT) Received: by mail-io0-f199.google.com with SMTP id m2so24722907ioa.3 for ; Tue, 19 Apr 2016 00:41:42 -0700 (PDT) Received: from lgeamrelo11.lge.com (LGEAMRELO11.lge.com. [156.147.23.51]) by mx.google.com with ESMTP id m6si2944240igx.88.2016.04.19.00.41.41 for ; Tue, 19 Apr 2016 00:41:41 -0700 (PDT) Date: Tue, 19 Apr 2016 16:42:39 +0900 From: Minchan Kim Subject: Re: [PATCH v3 08/16] zsmalloc: squeeze freelist into page->mapping Message-ID: <20160419074239.GB18448@bbox> References: <1459321935-3655-1-git-send-email-minchan@kernel.org> <1459321935-3655-9-git-send-email-minchan@kernel.org> <20160417155621.GE575@swordfish> MIME-Version: 1.0 In-Reply-To: <20160417155621.GE575@swordfish> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: Sergey Senozhatsky Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, jlayton@poochiereds.net, bfields@fieldses.org, Vlastimil Babka , Joonsoo Kim , koct9i@gmail.com, aquini@redhat.com, virtualization@lists.linux-foundation.org, Mel Gorman , Hugh Dickins , Rik van Riel , rknize@motorola.com, Gioh Kim , Sangseok Lee , Chan Gyun Jeong , Al Viro , YiPing Xu On Mon, Apr 18, 2016 at 12:56:21AM +0900, Sergey Senozhatsky wrote: > Hello, > > On (03/30/16 16:12), Minchan Kim wrote: > [..] > > +static void objidx_to_page_and_offset(struct size_class *class, > > + struct page *first_page, > > + unsigned long obj_idx, > > + struct page **obj_page, > > + unsigned long *offset_in_page) > > { > > - unsigned long obj; > > + int i; > > + unsigned long offset; > > + struct page *cursor; > > + int nr_page; > > > > - if (!page) { > > - VM_BUG_ON(obj_idx); > > - return NULL; > > - } > > + offset = obj_idx * class->size; > > so we already know the `offset' before we call objidx_to_page_and_offset(), > thus we can drop `struct size_class *class' and `obj_idx', and pass > `long obj_offset' (which is `obj_idx * class->size') instead, right? > > we also _may be_ can return `cursor' from the function. > > static struct page *objidx_to_page_and_offset(struct page *first_page, > unsigned long obj_offset, > unsigned long *offset_in_page); > > this can save ~20 instructions, which is not so terrible for a hot path > like obj_malloc(). what do you think? > > well, seems that `unsigned long *offset_in_page' can be calculated > outside of this function too, it's basically > > *offset_in_page = (obj_idx * class->size) & ~PAGE_MASK; > > so we don't need to supply it to this function, nor modify it there. > which can save ~40 instructions on my system. does this sound silly? Sound smart. :) At least, we will use it in hot path. Thanks! -- 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