From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oa0-f48.google.com (mail-oa0-f48.google.com [209.85.219.48]) by kanga.kvack.org (Postfix) with ESMTP id 7DEC46B0031 for ; Mon, 16 Jun 2014 15:34:51 -0400 (EDT) Received: by mail-oa0-f48.google.com with SMTP id m1so6276686oag.7 for ; Mon, 16 Jun 2014 12:34:51 -0700 (PDT) Received: from g2t2352.austin.hp.com (g2t2352.austin.hp.com. [15.217.128.51]) by mx.google.com with ESMTPS id h8si16831287obe.74.2014.06.16.12.34.50 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Mon, 16 Jun 2014 12:34:50 -0700 (PDT) Message-ID: <539F46D7.6050502@hp.com> Date: Mon, 16 Jun 2014 15:34:47 -0400 From: Waiman Long MIME-Version: 1.0 Subject: Re: [PATCH] mm: Move __vma_address() to internal.h to be inlined in huge_memory.c References: <1402600540-52031-1-git-send-email-Waiman.Long@hp.com> <20140612122546.cfdebdb22bb22c0f767e30b5@linux-foundation.org> <539A1CDA.5000709@hp.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Andrew Morton , Mel Gorman , Rik van Riel , Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Scott J Norton On 06/12/2014 05:45 PM, David Rientjes wrote: > On Thu, 12 Jun 2014, Waiman Long wrote: > >>>> The vma_address() function which is used to compute the virtual address >>>> within a VMA is used only by 2 files in the mm subsystem - rmap.c and >>>> huge_memory.c. This function is defined in rmap.c and is inlined by >>>> its callers there, but it is also declared as an external function. >>>> >>>> However, the __split_huge_page() function which calls vma_address() >>>> in huge_memory.c is calling it as a real function call. This is not >>>> as efficient as an inlined function. This patch moves the underlying >>>> inlined __vma_address() function to internal.h to be shared by both >>>> the rmap.c and huge_memory.c file. >>> This increases huge_memory.o's text+data_bss by 311 bytes, which makes >>> me suspect that it is a bad change due to its increase of kernel cache >>> footprint. >>> >>> Perhaps we should be noinlining __vma_address()? >> On my test machine, I saw an increase of 144 bytes in the text segment >> of huge_memory.o. The size in size is caused by an increase in the size >> of the __split_huge_page function. When I remove the >> >> if (unlikely(is_vm_hugetlb_page(vma))) >> pgoff = page->index<< huge_page_order(page_hstate(page)); >> >> check, the increase in size drops down to 24 bytes. As a THP cannot be >> a hugetlb page, there is no point in doing this check for a THP. I will >> update the patch to pass in an additional argument to disable this >> check for __split_huge_page. >> > I think we're seeking a reason or performance numbers that suggest > __vma_address() being inline is appropriate and so far we lack any such > evidence. Adding additional parameters to determine checks isn't going to > change the fact that it increases text size needlessly. This patch was motivated by my investigation of a freeze problem of an application running on SLES11 sp3 which was caused by the long time it took to munmap part of a THP. Inlining vma_address help a bit in that situation. However, the problem will be essentially gone after including patches that changing the anon_vma_chain to use rbtree instead of a simple list. I do agree that performance impact of inlining vma_address in minimal in the latest kernel. So I am not going to pursue this any further. Thank for the review. -Longman -- 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