This flag changes the reserve_bootmem() function to accept a new flag

BOOTMEM_EXCLUSIVE. If that flag is set, the function returns with

-EBUSY if the memory already has been reserved in the past. This is to

avoid conflicts.
IMPORTANT: The patch is only proof of concept. This means that it's only for

x86 and breaks other architectures. If the patch is ok, I'll change all other

architectures, too.
Signed-off-by: Bernhard Walle <bwalle@suse.de>
---

 arch/x86/kernel/mpparse_32.c |    4 ++--

 arch/x86/kernel/setup_32.c   |   12 ++++++------

 arch/x86/kernel/setup_64.c   |    2 +-

 include/linux/bootmem.h      |   13 ++++++++++++-

 mm/bootmem.c                 |   15 ++++++++++-----

 5 files changed, 31 insertions(+), 15 deletions(-)
--- a/arch/x86/kernel/mpparse_32.c

+++ b/arch/x86/kernel/mpparse_32.c

@@ -736,7 +736,7 @@ static int __init smp_scan_config (unsig

 			smp_found_config = 1;

 			printk(KERN_INFO "found SMP MP-table at %08lx\n",

 						virt_to_phys(mpf));

-			reserve_bootmem(virt_to_phys(mpf), PAGE_SIZE);

+			reserve_bootmem(virt_to_phys(mpf), PAGE_SIZE, 0);

 			if (mpf->mpf_physptr) {

 				/*

 				 * We cannot access to MPC table to compute

@@ -751,7 +751,7 @@ static int __init smp_scan_config (unsig

 				unsigned long end = max_low_pfn * PAGE_SIZE;

 				if (mpf->mpf_physptr + size > end)

 					size = end - mpf->mpf_physptr;

-				reserve_bootmem(mpf->mpf_physptr, size);

+				reserve_bootmem(mpf->mpf_physptr, size, 0);

 			}
 			mpf_found = mpf;

--- a/arch/x86/kernel/setup_32.c

+++ b/arch/x86/kernel/setup_32.c

@@ -317,7 +317,7 @@ static void __init reserve_ebda_region(v

 	unsigned int addr;

 	addr = get_bios_ebda();

 	if (addr)

-		reserve_bootmem(addr, PAGE_SIZE);

+		reserve_bootmem(addr, PAGE_SIZE, 0);

 }
 #ifndef CONFIG_NEED_MULTIPLE_NODES

@@ -439,13 +439,13 @@ void __init setup_bootmem_allocator(void

 	 * bootmem allocator with an invalid RAM area.

 	 */

 	reserve_bootmem(__pa_symbol(_text), (PFN_PHYS(min_low_pfn) +

...
[ message continues ]

I think we should unreserve the chunks of memory we have reserved so

far (Memory reserved from sidx to i), in case of error.
Thanks

Vivek

-

True. Next version is coming.
Thanks,

   Bernhard

-

Unfortunately, that's not possible without using a lock (or counters

instead of a bitmap) any more. If we just do
	for (i--; i >= sidx; i--)

		clear_bit(i, bdata->node_bootmem_map);
then another thread of execution could reserve the memory (without

BOOTMEM_EXCLUSIVE) in between -- and the code would free the memory

which is already reserved.
I think that could be modelled with a rwlock, not changing the default

case where BOOTMEM_EXCLUSIVE is not specified.
Thanks,

   Bernhard

-

On Wed, Oct 17, 2007 at 01:36:51PM +0200, Bernhard Walle wrote:
SMP initialization takes place after bootmem allocator has retired. That

would mean only one thread will be using bootmem allocator. Hence I think

unreserving memory without any kind of locking should be safe.
Thanks

Vivek

-

Could you give all of these 0's a name?  I really hate seeing random

magic numbers in these things.  0 completely kills the ability of

someone to read the code and figure out what it is trying to do without

going and looking at reserve_bootmem().
Or, alternatively, do something like this:
-extern void reserve_bootmem(unsigned long addr, unsigned long size);

+/*

+ * If flags is 0, then the return value is always 0 (success). If

+ * flags contains BOOTMEM_EXCLUSIVE, then -EBUSY is returned if the

+ * memory already was reserved.

+ */

+extern int reserve_bootmem(unsigned long addr, unsigned long size, int flag);

+int reserve_bootmem(unsigned long addr, unsigned long size)

+{

+	/* the 0 is because we don't

+	return reserve_bootmem_exclusive(addr, size, 0);

+}
Where all of the existing callers stay the same.  But, the ones wanting

exclusive access actually call the _exclusive() variant.  
-- Dave
-

Hi,
Andi was against more bootmem functions. ;)
Thanks,

   Bernhard

-

Yeah, I can't really blame him.
-- Dave
-