linux-kernel - Re: [RFC 0/2] Rootmem: boot-time memory allocator

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Message-ID: <20080503175426.GB5292@elte.hu>
Date:	Sat, 3 May 2008 19:54:26 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Johannes Weiner <hannes@...urebad.de>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC 0/2] Rootmem: boot-time memory allocator


* Johannes Weiner <hannes@...urebad.de> wrote:

> I was spending some time and work on the bootmem allocator the last 
> few weeks and came to the conclusion that its current design is not 
> appropriate anymore.
> 
> As Ingo said in another email, NUMA technologies will become weirder, 
> nodes whose PFNs span other nodes for example and it makes bootmem 
> code become an unreadable mess.
> 
> So I sat down two days ago and rewrote the allocator, here is the 
> result: rootmem!

hehe :-)

> The biggest difference to the old design is that there is only one 
> bitmap for all PFNs of all nodes together, so the overlapping PFN 
> problems simply dissolve and fun like allocations crossing node 
> boundaries work implicitely.  The new API requires every node used by 
> the allocator to be registered and after that the bitmap gets 
> allocated and the allocator enabled.
> 
> I chose to add a new allocator rather than replacing bootmem at once 
> because that would have required all callsites to switch in one go, 
> which would be a lot.  The new allocator can be adopted more slowly 
> and I added a compatibility API for everything besides actually 
> setting up the allocator.  When the last user dies, bootmem can be 
> dropped completely (including pgdat->bdata, whee..)
> 
> The main ideas from bootmem have been stolen^W preserved but the new 
> design allowed me to shrink the code a lot and express things more 
> simple and clear:
> 
> $ sloc.awk < mm/bootmem.c
> 455 lines of code, 65 lines of comments (520 lines total)
> 
> $ sloc.awk < mm/rootmem.c
> 243 lines of code, 96 lines of comments (339 lines total)

amazing!

i'd still suggest to keep it all named bootmem though :-/ How about 
bootmem2.c and then renaming it back to bootmem.c, once the last user is 
gone? That would save people from having to rename whole chapters in 
entire books ;-)

	Ingo
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