From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754671AbeDML1S (ORCPT ); Fri, 13 Apr 2018 07:27:18 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:56850 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754045AbeDML1O (ORCPT ); Fri, 13 Apr 2018 07:27:14 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org BFC0F605A8 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=cpandya@codeaurora.org Subject: Re: [PATCH] mm: vmalloc: Remove double execution of vunmap_page_range To: Michal Hocko Cc: Anshuman Khandual , vbabka@suse.cz, labbott@redhat.com, catalin.marinas@arm.com, hannes@cmpxchg.org, f.fainelli@gmail.com, xieyisheng1@huawei.com, ard.biesheuvel@linaro.org, richard.weiyang@gmail.com, byungchul.park@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1523611019-17679-1-git-send-email-cpandya@codeaurora.org> <8da9f826-2a3d-e618-e512-4fc8d45c16f2@codeaurora.org> <20180413110949.GA17670@dhcp22.suse.cz> From: Chintan Pandya Message-ID: <696fedc5-6bcd-f0a0-62f5-4f9e7b7c602a@codeaurora.org> Date: Fri, 13 Apr 2018 16:57:06 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180413110949.GA17670@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/13/2018 4:39 PM, Michal Hocko wrote: > On Fri 13-04-18 16:15:26, Chintan Pandya wrote: >> >> >> On 4/13/2018 4:10 PM, Anshuman Khandual wrote: >>> On 04/13/2018 03:47 PM, Chintan Pandya wrote: >>>> >>>> >>>> On 4/13/2018 3:29 PM, Anshuman Khandual wrote: >>>>> On 04/13/2018 02:46 PM, Chintan Pandya wrote: >>>>>> Unmap legs do call vunmap_page_range() irrespective of >>>>>> debug_pagealloc_enabled() is enabled or not. So, remove >>>>>> redundant check and optional vunmap_page_range() routines. >>>>> >>>>> vunmap_page_range() tears down the page table entries and does >>>>> not really flush related TLB entries normally unless page alloc >>>>> debug is enabled where it wants to make sure no stale mapping is >>>>> still around for debug purpose. Deferring TLB flush improves >>>>> performance. This patch will force TLB flush during each page >>>>> table tear down and hence not desirable. >>>>> >>>> Deferred TLB invalidation will surely improve performance. But force >>>> flush can help in detecting invalid access right then and there. I >>> >>> Deferred TLB invalidation was a choice made some time ago with the >>> commit db64fe02258f1507e ("mm: rewrite vmap layer") as these vmalloc >>> mappings wont be used other than inside the kernel and TLB gets >>> flushed when they are reused. This way it can still avail the benefit >>> of deferred TLB flushing without exposing itself to invalid accesses. >>> >>>> chose later. May be I should have clean up the vmap tear down code >>>> as well where it actually does the TLB invalidation. >>>> >>>> Or make TLB invalidation in free_unmap_vmap_area() be dependent upon >>>> debug_pagealloc_enabled(). >>> >>> Immediate TLB invalidation needs to be dependent on debug_pagealloc_ >>> enabled() and should be done only for debug purpose. Contrary to that >>> is not desirable. >>> >> Okay. I will raise v2 for that. > > More importantly. Your changelog absolutely lacks the _why_ part. It > just states what the code does which is not all that hard to read from > the diff. It is usually much more important to present _why_ the patch > is an improvement and worth merging. > It is improving performance in debug scenario. More than that, I see it as a clean up. Sure, I will try to address *why* in next change log. Chintan -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project