From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id 88F386B0005 for ; Fri, 13 Apr 2018 06:45:34 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id i137so4605288pfe.0 for ; Fri, 13 Apr 2018 03:45:34 -0700 (PDT) Received: from smtp.codeaurora.org (smtp.codeaurora.org. [198.145.29.96]) by mx.google.com with ESMTPS id y7si4180288pfl.313.2018.04.13.03.45.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 13 Apr 2018 03:45:33 -0700 (PDT) Subject: Re: [PATCH] mm: vmalloc: Remove double execution of vunmap_page_range References: <1523611019-17679-1-git-send-email-cpandya@codeaurora.org> <8da9f826-2a3d-e618-e512-4fc8d45c16f2@codeaurora.org> From: Chintan Pandya Message-ID: Date: Fri, 13 Apr 2018 16:15:26 +0530 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: 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 Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org 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. 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