Re: [bch-nvm-pages v9 2/6] bcache: initialize the nvm pages allocator

[Randy Dunlap <rdunlap@infradead.org>]

Hi,

On 4/28/21 2:39 PM, Qiaowei Ren wrote:
> From: Jianpeng Ma <jianpeng.ma@intel.com>
> 
> This patch define the prototype data structures in memory and initializes
> the nvm pages allocator.
> 
> The nvm address space which is managed by this allocatior can consist of

                                                 allocator

> many nvm namespaces, and some namespaces can compose into one nvm set,
> like cache set. For this initial implementation, only one set can be
> supported.
> 
> The users of this nvm pages allocator need to call regiseter_namespace()

                                                     register_namespace()

> to register the nvdimm device (like /dev/pmemX) into this allocator as
> the instance of struct nvm_namespace.
> 
> v9:
>   -Fix Kconfig dependance error(Reported-by Randy)

                 dependence

>   -Fix an uninitialized return value(Colin)
> 
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>
> Co-developed-by: Qiaowei Ren <qiaowei.ren@intel.com>
> Signed-off-by: Qiaowei Ren <qiaowei.ren@intel.com>
> Signed-off-by: Coly Li <colyli@suse.de>
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  drivers/md/bcache/Kconfig     |   8 +
>  drivers/md/bcache/Makefile    |   2 +-
>  drivers/md/bcache/nvm-pages.c | 285 ++++++++++++++++++++++++++++++++++
>  drivers/md/bcache/nvm-pages.h |  74 +++++++++
>  drivers/md/bcache/super.c     |   3 +
>  5 files changed, 371 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/md/bcache/nvm-pages.c
>  create mode 100644 drivers/md/bcache/nvm-pages.h
> 
> diff --git a/drivers/md/bcache/Kconfig b/drivers/md/bcache/Kconfig
> index d1ca4d059c20..3057da4cf8ff 100644
> --- a/drivers/md/bcache/Kconfig
> +++ b/drivers/md/bcache/Kconfig
> @@ -35,3 +35,11 @@ config BCACHE_ASYNC_REGISTRATION
>  	device path into this file will returns immediately and the real
>  	registration work is handled in kernel work queue in asynchronous
>  	way.
> +
> +config BCACHE_NVM_PAGES
> +	bool "NVDIMM support for bcache (EXPERIMENTAL)"
> +	depends on BCACHE
> +	depends on LIBNVDIMM
> +	depends on DAX
> +	help
> +	nvm pages allocator for bcache.
> diff --git a/drivers/md/bcache/Makefile b/drivers/md/bcache/Makefile
> index 5b87e59676b8..948e5ed2ca66 100644
> --- a/drivers/md/bcache/Makefile
> +++ b/drivers/md/bcache/Makefile
> @@ -4,4 +4,4 @@ obj-$(CONFIG_BCACHE)	+= bcache.o
>  
>  bcache-y		:= alloc.o bset.o btree.o closure.o debug.o extents.o\
>  	io.o journal.o movinggc.o request.o stats.o super.o sysfs.o trace.o\
> -	util.o writeback.o features.o
> +	util.o writeback.o features.o nvm-pages.o

This is not the right way to add an optional piece of code (nvm-pages.o)
to the full linked binary.

I.e., it is added unconditionally here and then inside its .c file, the
entire file is bracketed with (see below):

#ifdef CONFIG_BCACHE_NVM_PAGES
...
#endif /* CONFIG_BCACHE_NVM_PAGES */


The right way to do this is in Kconfig and Makefile changes alone,
and then nvm-pages.c does not need that huge #ifdef/#endif bracketing.


Documentation/kbuild/*.rst has some references to this, but it's probably
easier just to look at some examples.

E.g., see drivers/usb/common/: Kconfig and Makefile and how CONFIG_TRACING
adds debug.o to the usb-common-y binary build.
Same for USB_LED_TRIG and led.o.


> diff --git a/drivers/md/bcache/nvm-pages.c b/drivers/md/bcache/nvm-pages.c
> new file mode 100644
> index 000000000000..976ab9002c17
> --- /dev/null
> +++ b/drivers/md/bcache/nvm-pages.c
> @@ -0,0 +1,285 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Nvdimm page-buddy allocator
> + *
> + * Copyright (c) 2021, Intel Corporation.
> + * Copyright (c) 2021, Qiaowei Ren <qiaowei.ren@intel.com>.
> + * Copyright (c) 2021, Jianpeng Ma <jianpeng.ma@intel.com>.
> + */
> +
> +#ifdef CONFIG_BCACHE_NVM_PAGES

[delete many lines]

> +
> +#endif /* CONFIG_BCACHE_NVM_PAGES */


The header (.h) file also probably needs some fixing up.


thanks.
-- 
~Randy