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From: Coly Li <colyli@suse.de>
To: "Huang, Ying" <ying.huang@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>, Jan Kara <jack@suse.com>,
	Hannes Reinecke <hare@suse.com>, Christoph Hellwig <hch@lst.de>,
	linux-bcache@vger.kernel.org, linux-block@vger.kernel.org,
	Jianpeng Ma <jianpeng.ma@intel.com>,
	Qiaowei Ren <qiaowei.ren@intel.com>,
	axboe@kernel.dk
Subject: Re: Ask help for code review (was Re: [PATCH 03/14] bcache: add initial data structures for nvm pages)
Date: Wed, 23 Jun 2021 12:32:04 +0800	[thread overview]
Message-ID: <b1597c54-16ea-c943-8af7-25c8eab342e9@suse.de> (raw)
In-Reply-To: <875yy6l2a1.fsf@yhuang6-desk2.ccr.corp.intel.com>

Hi Ying,

I reply your comment in-place where you commented on.

On 6/22/21 4:41 PM, Huang, Ying wrote:
> Coly Li <colyli@suse.de> writes:
>
>> Hi all my dear receivers (Christoph, Dan, Hannes, Jan and Ying),
>>
>> I do need your help on code review for the following patch. This
>> series are posted and refined for 2 merge windows already but we
>> are lack of code review from more experienced kernel developers
>> like you all.
>>
>> The following patch defines a set of on-NVDIMM memory objects,
>> which are used to support NVDIMM for bcache journalling. Currently
>> the testing hardware is Intel AEP (Apache Pass).
>>
>> Qiangwei Ren and Jianpeng Ma work with me to compose a mini pages
>> allocator for NVDIMM pages, then we allocate non-volatiled memory
>> pages from NVDIMM to store bcache journal set. Then the jouranling
>> can be very fast and after system reboots, once the NVDIMM mapping
>> is done, bcache code can directly reference journal set memory
>> object without loading them via block layer interface.
>>
>> In order to restore allocated non-volatile memory, we use a set of
>> list (named owner list) to trace all allocated non-volatile memory
>> pages identified by UUID. Just like the bcache journal set, the list
>> stored in NVDIMM and accessed directly as typical in-memory list,
>> the only difference is they are non-volatiled: we access the lists
>> directly from NVDIMM, update the list in-place.
>>
>> This is why you can see pointers are defined in struct
>> bch_nvm_pgalloc_recs, because such object is reference directly as
>> memory object, and stored directly onto NVDIMM.
>>
>> Current patch series works as expected with limited data-set on
>> both bcache-tools and patched kernel. Because the bcache btree nodes
>> are not stored onto NVDIMM yet, journaling for leaf node splitting
>> will be handled in later series.
>>
>> The whole work of supporting NVDIMM for bcache will involve in,
>> - Storing bcache journal on NVDIMM
>> - Store bcache btree nodes on NVDIMM
>> - Store cached data on NVDIMM.
>> - On-NVDIMM objects consistency for power failure
>>
>> In order to make the code review to be more easier, the first step
>> we submit storing journal on NVDIMM into upstream firstly, following
>> work will be submitted step by step.
>>
>> Jens wants more widely review before taking this series into bcache
>> upstream, and you are all the experts I trust and have my respect.
>>
>> I do ask for help of code review from you all. Especially for the
>> following particular data structure definition patch, because I
>> define pointers in memory structures and reference and store them on
>> the NVDIMM.
>>
>> Thanks in advance for your help.
>>
>> Coly Li
>>
>>
>>
>>
>> On 6/15/21 1:49 PM, Coly Li wrote:
>>> This patch initializes the prototype data structures for nvm pages
>>> allocator,
>>>
>>> - struct bch_nvm_pages_sb
>>> This is the super block allocated on each nvdimm namespace. A nvdimm
>>> set may have multiple namespaces, bch_nvm_pages_sb->set_uuid is used
>>> to mark which nvdimm set this name space belongs to. Normally we will
>>> use the bcache's cache set UUID to initialize this uuid, to connect this
>>> nvdimm set to a specified bcache cache set.
>>>
>>> - struct bch_owner_list_head
>>> This is a table for all heads of all owner lists. A owner list records
>>> which page(s) allocated to which owner. After reboot from power failure,
>>> the ownwer may find all its requested and allocated pages from the owner
>>> list by a handler which is converted by a UUID.
>>>
>>> - struct bch_nvm_pages_owner_head
>>> This is a head of an owner list. Each owner only has one owner list,
>>> and a nvm page only belongs to an specific owner. uuid[] will be set to
>>> owner's uuid, for bcache it is the bcache's cache set uuid. label is not
>>> mandatory, it is a human-readable string for debug purpose. The pointer
>>> *recs references to separated nvm page which hold the table of struct
>>> bch_nvm_pgalloc_rec.
>>>
>>> - struct bch_nvm_pgalloc_recs
>>> This struct occupies a whole page, owner_uuid should match the uuid
>>> in struct bch_nvm_pages_owner_head. recs[] is the real table contains all
>>> allocated records.
>>>
>>> - struct bch_nvm_pgalloc_rec
>>> Each structure records a range of allocated nvm pages.
>>>   - Bits  0 - 51: is pages offset of the allocated pages.
>>>   - Bits 52 - 57: allocaed size in page_size * order-of-2
>>>   - Bits 58 - 63: reserved.
>>> Since each of the allocated nvm pages are power of 2, using 6 bits to
>>> represent allocated size can have (1<<(1<<64) - 1) * PAGE_SIZE maximum
>>> value. It can be a 76 bits width range size in byte for 4KB page size,
>>> which is large enough currently.
>>>
>>> Signed-off-by: Coly Li <colyli@suse.de>
>>> Cc: Jianpeng Ma <jianpeng.ma@intel.com>
>>> Cc: Qiaowei Ren <qiaowei.ren@intel.com>
>>> ---
>>>  include/uapi/linux/bcache-nvm.h | 200 ++++++++++++++++++++++++++++++++
>>>  1 file changed, 200 insertions(+)
>>>  create mode 100644 include/uapi/linux/bcache-nvm.h
>>>
>>> diff --git a/include/uapi/linux/bcache-nvm.h b/include/uapi/linux/bcache-nvm.h
>>> new file mode 100644
>>> index 000000000000..5094a6797679
>>> --- /dev/null
>>> +++ b/include/uapi/linux/bcache-nvm.h
>>> @@ -0,0 +1,200 @@
>>> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
>>> +
>>> +#ifndef _UAPI_BCACHE_NVM_H
>>> +#define _UAPI_BCACHE_NVM_H
>>> +
>>> +#if (__BITS_PER_LONG == 64)
>>> +/*
>>> + * Bcache on NVDIMM data structures
>>> + */
>>> +
>>> +/*
>>> + * - struct bch_nvm_pages_sb
>>> + *   This is the super block allocated on each nvdimm namespace. A nvdimm
>>> + * set may have multiple namespaces, bch_nvm_pages_sb->set_uuid is used to mark
>>> + * which nvdimm set this name space belongs to. Normally we will use the
>>> + * bcache's cache set UUID to initialize this uuid, to connect this nvdimm
>>> + * set to a specified bcache cache set.
>>> + *
>>> + * - struct bch_owner_list_head
>>> + *   This is a table for all heads of all owner lists. A owner list records
>>> + * which page(s) allocated to which owner. After reboot from power failure,
>>> + * the ownwer may find all its requested and allocated pages from the owner
>>> + * list by a handler which is converted by a UUID.
>>> + *
>>> + * - struct bch_nvm_pages_owner_head
>>> + *   This is a head of an owner list. Each owner only has one owner list,
>>> + * and a nvm page only belongs to an specific owner. uuid[] will be set to
>>> + * owner's uuid, for bcache it is the bcache's cache set uuid. label is not
>>> + * mandatory, it is a human-readable string for debug purpose. The pointer
>>> + * recs references to separated nvm page which hold the table of struct
>>> + * bch_pgalloc_rec.
>>> + *
>>> + *- struct bch_nvm_pgalloc_recs
>>> + *  This structure occupies a whole page, owner_uuid should match the uuid
>>> + * in struct bch_nvm_pages_owner_head. recs[] is the real table contains all
>>> + * allocated records.
>>> + *
>>> + * - struct bch_pgalloc_rec
>>> + *   Each structure records a range of allocated nvm pages. pgoff is offset
>>> + * in unit of page size of this allocated nvm page range. The adjoint page
>>> + * ranges of same owner can be merged into a larger one, therefore pages_nr
>>> + * is NOT always power of 2.
>>> + *
>>> + *
>>> + * Memory layout on nvdimm namespace 0
>>> + *
>>> + *    0 +---------------------------------+
>>> + *      |                                 |
>>> + *  4KB +---------------------------------+
>>> + *      |         bch_nvm_pages_sb        |
>>> + *  8KB +---------------------------------+ <--- bch_nvm_pages_sb.bch_owner_list_head
>>> + *      |       bch_owner_list_head       |
>>> + *      |                                 |
>>> + * 16KB +---------------------------------+ <--- bch_owner_list_head.heads[0].recs[0]
>>> + *      |       bch_nvm_pgalloc_recs      |
>>> + *      |  (nvm pages internal usage)     |
>>> + * 24KB +---------------------------------+
>>> + *      |                                 |
>>> + *      |                                 |
>>> + * 16MB  +---------------------------------+
>>> + *      |      allocable nvm pages        |
>>> + *      |      for buddy allocator        |
>>> + * end  +---------------------------------+
>>> + *
>>> + *
>>> + *
>>> + * Memory layout on nvdimm namespace N
>>> + * (doesn't have owner list)
>>> + *
>>> + *    0 +---------------------------------+
>>> + *      |                                 |
>>> + *  4KB +---------------------------------+
>>> + *      |         bch_nvm_pages_sb        |
>>> + *  8KB +---------------------------------+
>>> + *      |                                 |
>>> + *      |                                 |
>>> + *      |                                 |
>>> + *      |                                 |
>>> + *      |                                 |
>>> + *      |                                 |
>>> + * 16MB  +---------------------------------+
>>> + *      |      allocable nvm pages        |
>>> + *      |      for buddy allocator        |
>>> + * end  +---------------------------------+
>>> + *
>>> + */
>>> +
>>> +#include <linux/types.h>
>>> +
>>> +/* In sectors */
>>> +#define BCH_NVM_PAGES_SB_OFFSET			4096
>>> +#define BCH_NVM_PAGES_OFFSET			(16 << 20)
>>> +
>>> +#define BCH_NVM_PAGES_LABEL_SIZE		32
>>> +#define BCH_NVM_PAGES_NAMESPACES_MAX		8
>>> +
>>> +#define BCH_NVM_PAGES_OWNER_LIST_HEAD_OFFSET	(8<<10)
>>> +#define BCH_NVM_PAGES_SYS_RECS_HEAD_OFFSET	(16<<10)
>>> +
>>> +#define BCH_NVM_PAGES_SB_VERSION		0
>>> +#define BCH_NVM_PAGES_SB_VERSION_MAX		0
>>> +
>>> +static const unsigned char bch_nvm_pages_magic[] = {
>>> +	0x17, 0xbd, 0x53, 0x7f, 0x1b, 0x23, 0xd6, 0x83,
>>> +	0x46, 0xa4, 0xf8, 0x28, 0x17, 0xda, 0xec, 0xa9 };
>>> +static const unsigned char bch_nvm_pages_pgalloc_magic[] = {
>>> +	0x39, 0x25, 0x3f, 0xf7, 0x27, 0x17, 0xd0, 0xb9,
>>> +	0x10, 0xe6, 0xd2, 0xda, 0x38, 0x68, 0x26, 0xae };
>>> +
>>> +/* takes 64bit width */
>>> +struct bch_pgalloc_rec {
>>> +	__u64	pgoff:52;
>>> +	__u64	order:6;
>>> +	__u64	reserved:6;
>>> +};
>>> +
>>> +struct bch_nvm_pgalloc_recs {
>>> +union {
>>> +	struct {
>>> +		struct bch_nvm_pages_owner_head	*owner;
>>> +		struct bch_nvm_pgalloc_recs	*next;
> I have concerns about using pointers directly in on-NVDIMM data
> structure too.  How can you guarantee the NVDIMM devices will be mapped
> to exact same virtual address across reboot?
>
> Best Regards,
> Huang, Ying


We use the NVDIMM name space as memory, and from our testing and
observation, the DAX mapping base address is consistent if the NVDIMM
address from e820 table does not change.

And from our testing and observation, the NVDIMM address from e820
table does not change when,
- NVDIMM and DRAM memory population does not change
- Install more NVDIMM and/or DRAM based on existing memory population
- NVDIMM always plugged in same slot location and no movement or swap
- No CPU remove and change

For 99.9%+ time when the hardware working healthily, the above condition
can be assumed. Therefore we choose to store whole linear address
(pointer) here, other than relative offset inside the NVDIMM name space.

For the 0.0?% condition if the NVDIMM address from e820 table changes,
because the last time DAX map address is stored in ns_start of struct
bch_nvm_pages_sb, if the new DAX mapping address is different from
ns_srart value, all pointers in the owner list can be updated by,
    new_addr = (old_addr - old_ns_start) + new_ns_start

The update can be very fast (and it can be power failure tolerant with
carefully coding) for. Therefore we decide to store full linear address
for directly memory access for 99%+ condition, and update the pointers
for the 0.0?% condition when DAX mapping address of the NVDIMM changes.

Handling DAX mapping address change is not current high priority task,
our next task after this series merged will be the power failure tolerance
of the owner list (from Intel developers) and storing bcache btree nodes
on NVDIMM pages (from me).

Thanks for your comments and review.

Coly Li


>>> +		unsigned char			magic[16];
>>> +		unsigned char			owner_uuid[16];
>>> +		unsigned int			size;
>>> +		unsigned int			used;
>>> +		unsigned long			_pad[4];
>>> +		struct bch_pgalloc_rec		recs[];
>>> +	};
>>> +	unsigned char				pad[8192];
>>> +};
>>> +};
>>> +
>>> +#define BCH_MAX_RECS					\
>>> +	((sizeof(struct bch_nvm_pgalloc_recs) -		\
>>> +	 offsetof(struct bch_nvm_pgalloc_recs, recs)) /	\
>>> +	 sizeof(struct bch_pgalloc_rec))
>>> +
>>> +struct bch_nvm_pages_owner_head {
>>> +	unsigned char			uuid[16];
>>> +	unsigned char			label[BCH_NVM_PAGES_LABEL_SIZE];
>>> +	/* Per-namespace own lists */
>>> +	struct bch_nvm_pgalloc_recs	*recs[BCH_NVM_PAGES_NAMESPACES_MAX];
>>> +};
>>> +
>>> +/* heads[0] is always for nvm_pages internal usage */
>>> +struct bch_owner_list_head {
>>> +union {
>>> +	struct {
>>> +		unsigned int			size;
>>> +		unsigned int			used;
>>> +		unsigned long			_pad[4];
>>> +		struct bch_nvm_pages_owner_head	heads[];
>>> +	};
>>> +	unsigned char				pad[8192];
>>> +};
>>> +};
>>> +#define BCH_MAX_OWNER_LIST				\
>>> +	((sizeof(struct bch_owner_list_head) -		\
>>> +	 offsetof(struct bch_owner_list_head, heads)) /	\
>>> +	 sizeof(struct bch_nvm_pages_owner_head))
>>> +
>>> +/* The on-media bit order is local CPU order */
>>> +struct bch_nvm_pages_sb {
>>> +	unsigned long				csum;
>>> +	unsigned long				ns_start;
>>> +	unsigned long				sb_offset;
>>> +	unsigned long				version;
>>> +	unsigned char				magic[16];
>>> +	unsigned char				uuid[16];
>>> +	unsigned int				page_size;
>>> +	unsigned int				total_namespaces_nr;
>>> +	unsigned int				this_namespace_nr;
>>> +	union {
>>> +		unsigned char			set_uuid[16];
>>> +		unsigned long			set_magic;
>>> +	};
>>> +
>>> +	unsigned long				flags;
>>> +	unsigned long				seq;
>>> +
>>> +	unsigned long				feature_compat;
>>> +	unsigned long				feature_incompat;
>>> +	unsigned long				feature_ro_compat;
>>> +
>>> +	/* For allocable nvm pages from buddy systems */
>>> +	unsigned long				pages_offset;
>>> +	unsigned long				pages_total;
>>> +
>>> +	unsigned long				pad[8];
>>> +
>>> +	/* Only on the first name space */
>>> +	struct bch_owner_list_head		*owner_list_head;
>>> +
>>> +	/* Just for csum_set() */
>>> +	unsigned int				keys;
>>> +	unsigned long				d[0];
>>> +};
>>> +#endif /* __BITS_PER_LONG == 64 */
>>> +
>>> +#endif /* _UAPI_BCACHE_NVM_H */


  reply	other threads:[~2021-06-23  4:32 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-15  5:49 [PATCH 00/14] bcache patches for Linux v5.14 Coly Li
2021-06-15  5:49 ` [PATCH 01/14] bcache: fix error info in register_bcache() Coly Li
2021-06-22  9:47   ` Hannes Reinecke
2021-06-15  5:49 ` [PATCH 02/14] md: bcache: Fix spelling of 'acquire' Coly Li
2021-06-22 10:03   ` Hannes Reinecke
2021-06-15  5:49 ` [PATCH 03/14] bcache: add initial data structures for nvm pages Coly Li
2021-06-21 16:17   ` Ask help for code review (was Re: [PATCH 03/14] bcache: add initial data structures for nvm pages) Coly Li
2021-06-22  8:41     ` Huang, Ying
2021-06-23  4:32       ` Coly Li [this message]
2021-06-23  6:53         ` Huang, Ying
2021-06-23  7:04           ` Christoph Hellwig
2021-06-23  7:19             ` Coly Li
2021-06-23  7:21               ` Christoph Hellwig
2021-06-23 10:05                 ` Coly Li
2021-06-23 11:16                   ` Coly Li
2021-06-23 11:49                   ` Christoph Hellwig
2021-06-23 12:09                     ` Coly Li
2021-06-22 10:19   ` [PATCH 03/14] bcache: add initial data structures for nvm pages Hannes Reinecke
2021-06-23  7:09     ` Coly Li
2021-06-15  5:49 ` [PATCH 04/14] bcache: initialize the nvm pages allocator Coly Li
2021-06-22 10:39   ` Hannes Reinecke
2021-06-23  5:26     ` Coly Li
2021-06-23  9:16       ` Hannes Reinecke
2021-06-23  9:34         ` Coly Li
2021-06-15  5:49 ` [PATCH 05/14] bcache: initialization of the buddy Coly Li
2021-06-22 10:45   ` Hannes Reinecke
2021-06-23  5:35     ` Coly Li
2021-06-23  5:46       ` Re[2]: " Pavel Goran
2021-06-23  6:03         ` Coly Li
2021-06-15  5:49 ` [PATCH 06/14] bcache: bch_nvm_alloc_pages() " Coly Li
2021-06-22 10:51   ` Hannes Reinecke
2021-06-23  6:02     ` Coly Li
2021-06-15  5:49 ` [PATCH 07/14] bcache: bch_nvm_free_pages() " Coly Li
2021-06-22 10:53   ` Hannes Reinecke
2021-06-23  6:06     ` Coly Li
2021-06-15  5:49 ` [PATCH 08/14] bcache: get allocated pages from specific owner Coly Li
2021-06-22 10:54   ` Hannes Reinecke
2021-06-23  6:08     ` Coly Li
2021-06-15  5:49 ` [PATCH 09/14] bcache: use bucket index to set GC_MARK_METADATA for journal buckets in bch_btree_gc_finish() Coly Li
2021-06-22 10:55   ` Hannes Reinecke
2021-06-23  6:09     ` Coly Li
2021-06-15  5:49 ` [PATCH 10/14] bcache: add BCH_FEATURE_INCOMPAT_NVDIMM_META into incompat feature set Coly Li
2021-06-22 10:59   ` Hannes Reinecke
2021-06-23  6:09     ` Coly Li
2021-06-15  5:49 ` [PATCH 11/14] bcache: initialize bcache journal for NVDIMM meta device Coly Li
2021-06-22 11:01   ` Hannes Reinecke
2021-06-23  6:17     ` Coly Li
2021-06-23  9:20       ` Hannes Reinecke
2021-06-23 10:14         ` Coly Li
2021-06-15  5:49 ` [PATCH 12/14] bcache: support storing bcache journal into " Coly Li
2021-06-22 11:03   ` Hannes Reinecke
2021-06-23  6:19     ` Coly Li
2021-06-15  5:49 ` [PATCH 13/14] bcache: read jset from NVDIMM pages for journal replay Coly Li
2021-06-22 11:04   ` Hannes Reinecke
2021-06-23  6:21     ` Coly Li
2021-06-15  5:49 ` [PATCH 14/14] bcache: add sysfs interface register_nvdimm_meta to register NVDIMM meta device Coly Li
2021-06-22 11:04   ` Hannes Reinecke
2021-06-21 15:14 ` [PATCH 00/14] bcache patches for Linux v5.14 Jens Axboe
2021-06-21 15:25   ` Coly Li
2021-06-21 15:27     ` Jens Axboe

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