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 9368C6B0279 for ; Tue, 30 May 2017 12:43:57 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id c6so103711287pfj.5 for ; Tue, 30 May 2017 09:43:57 -0700 (PDT) Received: from mga07.intel.com (mga07.intel.com. [134.134.136.100]) by mx.google.com with ESMTPS id e11si45287002pln.291.2017.05.30.09.43.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 30 May 2017 09:43:56 -0700 (PDT) Date: Tue, 30 May 2017 10:43:55 -0600 From: Ross Zwisler Subject: Re: [HMM 07/15] mm/ZONE_DEVICE: new type of ZONE_DEVICE for unaddressable memory v3 Message-ID: <20170530164355.GA25891@linux.intel.com> References: <20170524172024.30810-1-jglisse@redhat.com> <20170524172024.30810-8-jglisse@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170524172024.30810-8-jglisse@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: =?iso-8859-1?B?Suly9G1l?= Glisse Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Dan Williams , "Kirill A . Shutemov" , John Hubbard , Ross Zwisler On Wed, May 24, 2017 at 01:20:16PM -0400, Jerome Glisse wrote: > HMM (heterogeneous memory management) need struct page to support migration > from system main memory to device memory. Reasons for HMM and migration to > device memory is explained with HMM core patch. > > This patch deals with device memory that is un-addressable memory (ie CPU > can not access it). Hence we do not want those struct page to be manage > like regular memory. That is why we extend ZONE_DEVICE to support different > types of memory. > > A persistent memory type is define for existing user of ZONE_DEVICE and a > new device un-addressable type is added for the un-addressable memory type. > There is a clear separation between what is expected from each memory type > and existing user of ZONE_DEVICE are un-affected by new requirement and new > use of the un-addressable type. All specific code path are protect with > test against the memory type. > > Because memory is un-addressable we use a new special swap type for when > a page is migrated to device memory (this reduces the number of maximum > swap file). > > The main two additions beside memory type to ZONE_DEVICE is two callbacks. > First one, page_free() is call whenever page refcount reach 1 (which means > the page is free as ZONE_DEVICE page never reach a refcount of 0). This > allow device driver to manage its memory and associated struct page. > > The second callback page_fault() happens when there is a CPU access to > an address that is back by a device page (which are un-addressable by the > CPU). This callback is responsible to migrate the page back to system > main memory. Device driver can not block migration back to system memory, > HMM make sure that such page can not be pin into device memory. > > If device is in some error condition and can not migrate memory back then > a CPU page fault to device memory should end with SIGBUS. > > Changed since v2: > - s/DEVICE_UNADDRESSABLE/DEVICE_PRIVATE > Changed since v1: > - rename to device private memory (from device unaddressable) > > Signed-off-by: Jerome Glisse > Acked-by: Dan Williams > Cc: Ross Zwisler > --- <> > @@ -35,18 +37,88 @@ static inline struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start) > } > #endif > > +/* > + * Specialize ZONE_DEVICE memory into multiple types each having differents > + * usage. > + * > + * MEMORY_DEVICE_PUBLIC: > + * Persistent device memory (pmem): struct page might be allocated in different > + * memory and architecture might want to perform special actions. It is similar > + * to regular memory, in that the CPU can access it transparently. However, > + * it is likely to have different bandwidth and latency than regular memory. > + * See Documentation/nvdimm/nvdimm.txt for more information. > + * > + * MEMORY_DEVICE_PRIVATE: > + * Device memory that is not directly addressable by the CPU: CPU can neither > + * read nor write _UNADDRESSABLE memory. In this case, we do still have struct _PRIVATE Just noticed that one holdover from the DEVICE_UNADDRESSABLE naming. > + * pages backing the device memory. Doing so simplifies the implementation, but > + * it is important to remember that there are certain points at which the struct > + * page must be treated as an opaque object, rather than a "normal" struct page. > + * A more complete discussion of unaddressable memory may be found in > + * include/linux/hmm.h and Documentation/vm/hmm.txt. > + */ > +enum memory_type { > + MEMORY_DEVICE_PUBLIC = 0, > + MEMORY_DEVICE_PRIVATE, > +}; -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org