Re: [PATCH] SQUASHME: Fixes to e820 handling of pmem

From: Christoph Hellwig <hch@lst.de>
To: Boaz Harrosh <boaz@plexistor.com>
Cc: Christoph Hellwig <hch@lst.de>,
	linux-nvdimm@ml01.01.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, x86@kernel.org, axboe@kernel.dk,
	ross.zwisler@linux.intel.com
Subject: Re: [PATCH] SQUASHME: Fixes to e820 handling of pmem
Date: Thu, 2 Apr 2015 11:30:37 +0200	[thread overview]
Message-ID: <20150402093037.GA14209@lst.de> (raw)
In-Reply-To: <551BFFD2.20608@plexistor.com>

On Wed, Apr 01, 2015 at 05:25:22PM +0300, Boaz Harrosh wrote:
>  		pfn = PFN_DOWN(ei->addr + ei->size);
>  
> -		switch (ei->type) {
> -		case E820_RAM:
> -		case E820_PRAM:
> -		case E820_RESERVED_KERN:
> -			break;
> -		default:
> +		if (ei->type != E820_RAM && ei->type != E820_RESERVED_KERN)
>  			register_nosave_region(PFN_UP(ei->addr), pfn);
> -		}

I guess this makes sense - if the content is persistent already we don't need
to save it.

> -		if (e820.map[i].type != E820_RESERVED || res->start < (1ULL<<20)) {
> -			if (e820.map[i].type != E820_PRAM)
> -				res->flags |= IORESOURCE_BUSY;
> +		if (((e820.map[i].type != E820_RESERVED) &&
> +		     (e820.map[i].type != E820_PRAM)) ||
> +		     res->start < (1ULL<<20)) {

So now we also trigger for PRAM regions under 1ULL<<20, was that the
intentional change?  Honestly I don't really understand this 1ULL<<20
magic here even for the existing case.  Guess this is magic from the
old ISA PC days?  

> +			res->flags |= IORESOURCE_BUSY;

Guess this is the real change, and I'd love to understand why this
makes a difference for you.  IORESOURCE_BUSY is checked almost never,
and is intented to mean it's a driver mapping.