Re: [Patch v2] kexec: increase max of kexec segments and use dynamicallocation

From: Cong Wang
Date: Thu Jul 29 2010 - 02:38:34 EST

On 07/27/10 18:00, Milton Miller wrote:
[ Added kexec at and linuxppc-dev@xxxxxxxxxxxxxxxx ]

Currently KEXEC_SEGMENT_MAX is only 16 which is too small for machine with
many memory ranges. When hibernate on a machine with disjoint memory we do
need one segment for each memory region. Increase this hard limit to 16K
which is reasonably large.

And change ->segment from a static array to a dynamically allocated memory.

Cc: Neil Horman<nhorman@xxxxxxxxxx>
Cc: huang ying<huang.ying.caritas@xxxxxxxxx>
Cc: Eric W. Biederman<ebiederm@xxxxxxxxxxxx>
Signed-off-by: WANG Cong<amwang@xxxxxxxxxx>

diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
index ed31a29..f115585 100644
--- a/arch/powerpc/kernel/machine_kexec_64.c
+++ b/arch/powerpc/kernel/machine_kexec_64.c
@@ -131,10 +131,7 @@ static void copy_segments(unsigned long ind)
void kexec_copy_flush(struct kimage *image)
long i, nr_segments = image->nr_segments;
- struct kexec_segment ranges[KEXEC_SEGMENT_MAX];
- /* save the ranges on the stack to efficiently flush the icache */
- memcpy(ranges, image->segment, sizeof(ranges));
+ struct kexec_segment range;

I'm glad you found our copy on the stack and removed the stack overflow
that comes with this bump, but ...

* After this call we may not use anything allocated in dynamic
@@ -148,9 +145,11 @@ void kexec_copy_flush(struct kimage *image)
* we need to clear the icache for all dest pages sometime,
* including ones that were in place on the original copy
- for (i = 0; i< nr_segments; i++)
- flush_icache_range((unsigned long)__va(ranges[i].mem),
- (unsigned long)__va(ranges[i].mem + ranges[i].memsz));
+ for (i = 0; i< nr_segments; i++) {
+ memcpy(&range,&image->segment[i], sizeof(range));
+ flush_icache_range((unsigned long)__va(range.mem),
+ (unsigned long)__va(range.mem + range.memsz));
+ }

This is executed after the copy, so as it says,
"we may not use anything allocated in dynamic memory".

We could allocate control pages to copy the segment list into.
Actually ppc64 doesn't use the existing control page, but that
is only 4kB today.

We need the list to icache flush all the pages in all the segments.
The as the indirect list doesn't have pages that were allocated at
their destination.

Or maybe the icache flush should be done in the generic code
like it does for crash load segments?

I don't get the point here, according to the comments,
it is copied into stack because of efficiency.

The opposite of love is not hate, it's indifference.
- Elie Wiesel
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