From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 9F0C46B0006 for ; Tue, 22 May 2018 15:58:24 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id j14-v6so11681005pfn.11 for ; Tue, 22 May 2018 12:58:24 -0700 (PDT) Received: from EUR02-AM5-obe.outbound.protection.outlook.com (mail-eopbgr00120.outbound.protection.outlook.com. [40.107.0.120]) by mx.google.com with ESMTPS id 89-v6si17499314plb.154.2018.05.22.12.58.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 22 May 2018 12:58:23 -0700 (PDT) Subject: Re: [PATCH v6 17/17] mm: Distinguish VMalloc pages References: <20180518194519.3820-1-willy@infradead.org> <20180518194519.3820-18-willy@infradead.org> <74e9bf39-ae17-cc00-8fca-c34b75675d49@virtuozzo.com> <20180522175836.GB1237@bombadil.infradead.org> From: Andrey Ryabinin Message-ID: Date: Tue, 22 May 2018 22:57:34 +0300 MIME-Version: 1.0 In-Reply-To: <20180522175836.GB1237@bombadil.infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: linux-mm@kvack.org, Matthew Wilcox , Andrew Morton , "Kirill A . Shutemov" , Christoph Lameter , Lai Jiangshan , Pekka Enberg , Vlastimil Babka , Dave Hansen , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= On 05/22/2018 08:58 PM, Matthew Wilcox wrote: > On Tue, May 22, 2018 at 07:10:52PM +0300, Andrey Ryabinin wrote: >> On 05/18/2018 10:45 PM, Matthew Wilcox wrote: >>> From: Matthew Wilcox >>> >>> For diagnosing various performance and memory-leak problems, it is helpful >>> to be able to distinguish pages which are in use as VMalloc pages. >>> Unfortunately, we cannot use the page_type field in struct page, as >>> this is in use for mapcount by some drivers which map vmalloced pages >>> to userspace. >>> >>> Use a special page->mapping value to distinguish VMalloc pages from >>> other kinds of pages. Also record a pointer to the vm_struct and the >>> offset within the area in struct page to help reconstruct exactly what >>> this page is being used for. >> >> This seems useless. page->vm_area and page->vm_offset are never used. >> There are no follow up patches which use this new information 'For diagnosing various performance and memory-leak problems', >> and no explanation how is it can be used in current form. > > Right now, it's by-hand. tools/vm/page-types.c will tell you which pages > are allocated to VMalloc. Many people use kernel debuggers, crashdumps > and similar to examine the kernel's memory. Leaving these breadcrumbs > is helpful, and those fields simply weren't in use before. > >> Also, this patch breaks code like this: >> if (mapping = page_mapping(page)) >> // access mapping > > Example of broken code, please? Pages allocated from the page allocator > with alloc_page() come with page->mapping == NULL. This code snippet > would not have granted access to vmalloc pages before. > Some implementation of the flush_dcache_page(), also set_page_dirty() can be called on userspace-mapped vmalloc pages during unmap - zap_pte_range() -> set_page_dirty()