From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 5E0D08E0001 for ; Thu, 27 Sep 2018 14:32:41 -0400 (EDT) Received: by mail-ed1-f71.google.com with SMTP id t24-v6so1598473eds.12 for ; Thu, 27 Sep 2018 11:32:41 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id h25-v6si3111534edw.256.2018.09.27.11.32.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 27 Sep 2018 11:32:39 -0700 (PDT) Date: Thu, 27 Sep 2018 20:32:36 +0200 From: Michal Hocko Subject: Re: [PATCH] mm: Introduce new function vm_insert_kmem_page Message-ID: <20180927183236.GJ6278@dhcp22.suse.cz> References: <20180927175123.GA16367@jordon-HP-15-Notebook-PC> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180927175123.GA16367@jordon-HP-15-Notebook-PC> Sender: owner-linux-mm@kvack.org List-ID: To: Souptick Joarder Cc: akpm@linux-foundation.org, dan.j.williams@intel.com, kirill.shutemov@linux.intel.com, pasha.tatashin@oracle.com, riel@redhat.com, willy@infradead.org, minchan@kernel.org, peterz@infradead.org, ying.huang@intel.com, ak@linux.intel.com, rppt@linux.vnet.ibm.com, linux@dominikbrodowski.net, arnd@arndb.de, mcgrof@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu 27-09-18 23:21:23, Souptick Joarder wrote: > vm_insert_kmem_page is similar to vm_insert_page and will > be used by drivers to map kernel (kmalloc/vmalloc/pages) > allocated memory to user vma. > > Previously vm_insert_page is used for both page fault > handlers and outside page fault handlers context. When > vm_insert_page is used in page fault handlers context, > each driver have to map errno to VM_FAULT_CODE in their > own way. But as part of vm_fault_t migration all the > page fault handlers are cleaned up by using new vmf_insert_page. > Going forward, vm_insert_page will be removed by converting > it to vmf_insert_page. > > But their are places where vm_insert_page is used outside > page fault handlers context and converting those to > vmf_insert_page is not a good approach as drivers will end > up with new VM_FAULT_CODE to errno conversion code and it will > make each user more complex. > > So this new vm_insert_kmem_page can be used to map kernel > memory to user vma outside page fault handler context. > > In short, vmf_insert_page will be used in page fault handlers > context and vm_insert_kmem_page will be used to map kernel > memory to user vma outside page fault handlers context. > > We will slowly convert all the user of vm_insert_page to > vm_insert_kmem_page after this API be available in linus tree. In general I do not like patches adding a new exports/functionality without any user added at the same time. I am not going to look at the implementation right now but the above opens more questions than it gives answers. Why do we have to distinguish #PF from other paths? -- Michal Hocko SUSE Labs