Re: [PATCH] powerpc: add support for PAGE_SIZEs greater than 4KB for

Hello Benjamin,

Benjamin Herrenschmidt wrote:

quoted

[snip]
    

quoted

diff --git a/arch/powerpc/kernel/head_booke.h b/arch/powerpc/kernel/head_booke.h
index fce2df9..4f802df 100644
--- a/arch/powerpc/kernel/head_booke.h
+++ b/arch/powerpc/kernel/head_booke.h

@@ -20,7 +20,9 @@
 	beq	1f;							     \
 	mfspr	r1,SPRN_SPRG3;		/* if from user, start at top of   */\
 	lwz	r1,THREAD_INFO-THREAD(r1); /* this thread's kernel stack   */\
-	addi	r1,r1,THREAD_SIZE;					     \
+	lis	r11,THREAD_SIZE@h;					     \
+	ori	r11,r11,THREAD_SIZE@l;					     \
+	add	r1,r1,r11;

\
      

It would be nice if we could avoid the extra instruction here when the
page sizes isn't big enough to require it.
    

As a matter of fact, I don't see why THREAD_SIZE should ever need that,
there is no reason to change the kernel stack size.
  

Well, this was introduced because of that:

kernel/fork.c [179]:

max_threads = mempages / (8 * THREAD_SIZE / PAGE_SIZE);

With THREAD_SIZE=8K we will get mempages divided by zero if PAGE_SIZE is bigger than 64K. (Well, another reason not to use >64K pages). Not sure this is the right way to fix it.

Regards, Ilya.