Re: [PATCH 2/3] x86: add a is_e820_ram() helper

From: Christoph Hellwig <hch@lst.de>
To: Yinghai Lu <yinghai@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Ingo Molnar <mingo@kernel.org>,
	linux-nvdimm@ml01.01.org, linux-fsdevel@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	ross.zwisler@linux.intel.com, Jens Axboe <axboe@kernel.dk>,
	boaz@plexistor.com
Subject: Re: [PATCH 2/3] x86: add a is_e820_ram() helper
Date: Fri, 27 Mar 2015 09:10:07 +0100	[thread overview]
Message-ID: <20150327081007.GA12909@lst.de> (raw)
In-Reply-To: <CAE9FiQUcESZOzLW7Jcc-g5xUMfxx-kJqgbOzyD4jA7QVDg7+=Q@mail.gmail.com>

On Thu, Mar 26, 2015 at 03:59:28PM -0700, Yinghai Lu wrote:
> What do you want to get here?
> 
> You did not modify memblock_x86_fill() to treat
> E820_PRAM as E820_RAM, so memblock will not have any
> entry for E820_PRAM, so you do not need to call memblock_reserve
> there.
> 
> And the same time,  init_memory_mapping() will call
> init_range_memory_mapping/for_each_mem_pfn_range() to
> set kernel mapping for memory range in memblock only.
> So here calling init_memory_mapping will not do anything.
> then just drop calling to that init_memory_mapping.
> --- so will not kernel mapping pmem, is that what you intended to have?

I think the intent of the old Intel code was to indeed map the pmem
into KVA space.  That got broken when I forward ported it to use
memblocks.  However the current pmem infrastructure doesn't need the
KVA mapping, so I can remove it for now.

However we have heated discussions about how to do I/O to pmem, and
KVA mapping is one of the options.  If we got with that option I might
bring this code back in a fixed up version.