linux-kernel - Re: [PATCH v2 08/23] mm/memblock: Add memblock memory allocation apis

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Message-ID: <52A0B42C.5080405@ti.com>
Date:	Thu, 5 Dec 2013 12:13:16 -0500
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Tejun Heo <tj@...nel.org>
CC:	Grygorii Strashko <grygorii.strashko@...com>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-mm@...ck.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 08/23] mm/memblock: Add memblock memory allocation
 apis

On Thursday 05 December 2013 11:59 AM, Tejun Heo wrote:
> Hello,
> 
> On Thu, Dec 05, 2013 at 03:12:30PM +0200, Grygorii Strashko wrote:
>> I'll try to provide more technical details here.
>> As Santosh mentioned in previous e-mails, it's not easy to simply
>> get rid of using MAX_NUMNODES:
>> 1) we introduce new interface memblock_allocX 
>> 2) our interface uses memblock APIs __next_free_mem_range_rev()
>>    and __next_free_mem_range()
>> 3) __next_free_mem_range_rev() and __next_free_mem_range() use MAX_NUMNODES
>> 4) _next_free_mem_range_rev() and __next_free_mem_range() are used standalone,
>>    outside of our interface as part of *for_each_free_mem_range* or for_each_mem_pfn_range ..
>>
>> The point [4] leads to necessity to find and correct all places where memmblock APIs
>> are used and where it's expected to get MAX_NUMNODES as input parameter.
>> The major problem is that simple "grep" will not work, because memmblock APIs calls
>> are hidden inside other MM modules and it's not always clear
>> what will be passed as input parameters to APIs of these MM modules
>> (for example sparse_memory_present_with_active_regions() or sparse.c).
> 
> Isn't that kinda trivial to work around?  Make those functions accept
> both MAX_NUMNODES and NUMA_NO_NODE but emit warning on MAX_NUMNODES
> (preferably throttled reasonably).  Given the history of API, we'd
> probably want to keep such warning for extended period of time but
> that's what we'd need to do no matter what.
> 
Looks a good idea.

>> As result, WIP patch, I did, and which was posted by Santosh illustrates
>> the probable size and complexity of the change.
> 
> Again, I don't really mind the order things happen but I don't think
> it's a good idea to spread misusage with a new API.  You gotta deal
> with it one way or the other.
> 
>> Sorry, but question here is not "Do or not to do?", but rather 'how to do?",
>> taking into account complexity and state of the current MM code.
>> For example. would it be ok if I'll workaround the issue as in the attached patch?
> 
> Well, it's more of when.  It's not really a technically difficult
> task and all I'm saying is it better be sooner than later.
> 
Fair enough. Based on your suggestion, we will try to see if
we can proceed with 4) accepting both MAX_NUMNODES and NUMA_NO_NODE.

Thanks for the suggestion.

regards,
Santosh

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