From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754597AbbA0WnW (ORCPT ); Tue, 27 Jan 2015 17:43:22 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:38942 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752758AbbA0WnV (ORCPT ); Tue, 27 Jan 2015 17:43:21 -0500 Date: Tue, 27 Jan 2015 14:43:19 -0800 From: Andrew Morton To: Sergei Rogachev Cc: iamjoonsoo.kim@lge.com, LKML Subject: Re: [PATCH 1/1] mm/page_ext: remove unnecessary stack_trace field Message-Id: <20150127144319.f3a161e5f5d562a0a605371e@linux-foundation.org> In-Reply-To: <1422309132-28030-2-git-send-email-rogachevsergei@gmail.com> References: <1422309132-28030-1-git-send-email-rogachevsergei@gmail.com> <1422309132-28030-2-git-send-email-rogachevsergei@gmail.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-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 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. --- 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; _