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

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Message-ID: <20150402093037.GA14209@lst.de>
Date:	Thu, 2 Apr 2015 11:30:37 +0200
From:	Christoph Hellwig <hch@....de>
To:	Boaz Harrosh <boaz@...xistor.com>
Cc:	Christoph Hellwig <hch@....de>, linux-nvdimm@...1.01.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, axboe@...nel.dk, ross.zwisler@...ux.intel.com
Subject: Re: [PATCH] SQUASHME: Fixes to e820 handling of pmem

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.
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