From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756029AbbA1U6x (ORCPT ); Wed, 28 Jan 2015 15:58:53 -0500 Received: from mail-lb0-f171.google.com ([209.85.217.171]:34917 "EHLO mail-lb0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755891AbbA1U6m (ORCPT ); Wed, 28 Jan 2015 15:58:42 -0500 Date: Wed, 28 Jan 2015 23:08:47 +0400 From: Sergei Rogachev To: Andrew Morton Cc: iamjoonsoo.kim@lge.com, LKML Subject: Re: [PATCH 1/1] mm/page_ext: remove unnecessary stack_trace field Message-Id: <20150128230847.16cc8e4fbb5f601dc667d94d@gmail.com> In-Reply-To: <20150127144319.f3a161e5f5d562a0a605371e@linux-foundation.org> References: <1422309132-28030-1-git-send-email-rogachevsergei@gmail.com> <1422309132-28030-2-git-send-email-rogachevsergei@gmail.com> <20150127144319.f3a161e5f5d562a0a605371e@linux-foundation.org> X-Mailer: Sylpheed 3.4.0beta5 (GTK+ 2.24.20; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 27 Jan 2015 14:43:19 -0800 Andrew Morton wrote: > On Tue, 27 Jan 2015 00:52:12 +0300 Sergei Rogachev wrote: > > > Page owner uses the page_ext structure to keep meta-information > > for every page in the system. The structure also contains a field > > of type 'struct stack_trace', page owner uses this field during > > invocation of the function save_stack_trace. It is easy to notice > > that keeping a copy of this structure for every page in the system > > is very inefficiently in terms of memory. > > > > The patch removes this unnecessary field of page_ext and forces > > page owner to use a stack_trace structure allocated on the stack. > > > > Fair enough. > > What do you think of the below tweaks? Seems a bit neater, and it will > cause all unmentioned fields to be zeroed out. It's not a bug to leave > .max_entries uninitialised in print_page_owner(), but it's nice not to > leave loose ends. Yes, with your fix the code looks much better! > > --- a/mm/page_owner.c~mm-page_ext-remove-unnecessary-stack_trace-field-fix > +++ a/mm/page_owner.c > @@ -59,15 +59,14 @@ void __reset_page_owner(struct page *pag > > void __set_page_owner(struct page *page, unsigned int order, gfp_t gfp_mask) > { > - struct page_ext *page_ext; > - struct stack_trace trace; > + struct page_ext *page_ext = lookup_page_ext(page); > + struct stack_trace trace = { > + .nr_entries = 0, > + .max_entries = ARRAY_SIZE(page_ext->trace_entries), > + .entries = &page_ext->trace_entries[0], > + .skip = 3, > + }; > > - page_ext = lookup_page_ext(page); > - > - trace.nr_entries = 0; > - trace.max_entries = ARRAY_SIZE(page_ext->trace_entries); > - trace.entries = &page_ext->trace_entries[0]; > - trace.skip = 3; > save_stack_trace(&trace); > > page_ext->order = order; > @@ -83,8 +82,11 @@ print_page_owner(char __user *buf, size_ > { > int ret; > int pageblock_mt, page_mt; > - struct stack_trace trace; > char *kbuf; > + struct stack_trace trace = { > + .nr_entries = page_ext->nr_entries, > + .entries = &page_ext->trace_entries[0], > + }; > > kbuf = kmalloc(count, GFP_KERNEL); > if (!kbuf) > @@ -122,9 +124,6 @@ print_page_owner(char __user *buf, size_ > if (ret >= count) > goto err; > > - trace.nr_entries = page_ext->nr_entries; > - trace.entries = &page_ext->trace_entries[0]; > - > ret += snprint_stack_trace(kbuf + ret, count - ret, &trace, 0); > if (ret >= count) > goto err; > _ >