From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754291AbeDMKkm (ORCPT ); Fri, 13 Apr 2018 06:40:42 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:46352 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753634AbeDMKkk (ORCPT ); Fri, 13 Apr 2018 06:40:40 -0400 Subject: Re: [PATCH] mm: vmalloc: Remove double execution of vunmap_page_range To: Chintan Pandya , 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 References: <1523611019-17679-1-git-send-email-cpandya@codeaurora.org> <8da9f826-2a3d-e618-e512-4fc8d45c16f2@codeaurora.org> Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org From: Anshuman Khandual Date: Fri, 13 Apr 2018 16:10:29 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <8da9f826-2a3d-e618-e512-4fc8d45c16f2@codeaurora.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 18041310-0020-0000-0000-000004117EDE X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18041310-0021-0000-0000-000042A5B0FF Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-13_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804130099 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.