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

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Message-ID: <86802c440805032106t4d020838v39aaf93309003cdb@mail.gmail.com>
Date:	Sat, 3 May 2008 21:06:02 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Johannes Weiner" <hannes@...urebad.de>,
	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

On Sat, May 3, 2008 at 10:54 AM, Ingo Molnar <mingo@...e.hu> wrote:
>
>  * 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 ;-)

for spanning support node0:0-2g, 4-6g; node1: 2-4g, 6-8g, could have
some problem.

+/*
+ * rootmem_register_node - register a node to rootmem
+ * @nid: node id
+ * @start: first pfn on the node
+ * @end: first pfn after the node
+ *
+ * This function must not be called anymore if the allocator
+ * is already up and running (rootmem_setup() has been called).
+ */
+void __init rootmem_register_node(int nid, unsigned long start,
+                       unsigned long end)
+{
+       BUG_ON(rootmem_functional);
+
+       if (start < rootmem_min_pfn)
+               rootmem_min_pfn = start;
+       if (end > rootmem_max_pfn)
+               rootmem_max_pfn = end;
+
+       rootmem_node_pages[nid] = end - start;
+       rootmem_node_offsets[nid] = start;
+       rootmem_nr_nodes++;
+}

could change rootmem_node_pages/offsets to be struct array with
offset, pages, and nid. and every node could several struct. and whole
array should be sorted with nid.

YH
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