Re: [PATCH] Reduce TLB flushing during process migration

[Jack Steiner <steiner@sgi.com>]

On Mon, May 24, 2004 at 10:26:12PM -0700, Andrew Morton wrote:
> Jack Steiner <steiner@sgi.com> wrote:
> >
> > Here is an updated patch for flushing the TLB on SN2 after a process
> >  migration. The patch is based on the latest "//linux.bkbits.net/linux-2.5"
> >  bitkeeper tree.
> 
> Instant oops on ia32 because p->mm is NULL for kernel threads.  You might
> want to check that on ia64 too - it's not clear to me why it works there.

                                                                                                                                     
On IA64, it is ok to call flush_tlb_mm() with a NULL mm. I not sure if
this is *suppose* to be part of the API for flush_tlb_mm() but it is
allowed on IA64.  flush_tlb_mm() has an explicit check for NULL mm & simply 
returns.
                                                                                                                                     
                                                                                                                                     
                                                                                                                                     
> 
> --- 25/include/asm-generic/tlb.h~reduce-tlb-flushing-during-process-migration-oops-fix	2004-05-24 22:20:30.018626600 -0700
> +++ 25-akpm/include/asm-generic/tlb.h	2004-05-24 22:21:12.621150032 -0700
> @@ -147,6 +147,10 @@ static inline void tlb_remove_page(struc
>  		__pmd_free_tlb(tlb, pmdp);			\
>  	} while (0)
>  
> -#define tlb_migrate_finish(mm) flush_tlb_mm(mm)
> +#define tlb_migrate_finish(mm)					\
> +	do {							\
> +		if (likely(mm))					\
> +			flush_tlb_mm(mm);			\
> +	} while (0)
>  
>  #endif /* _ASM_GENERIC__TLB_H */
> 
> 
> But I don't understand why your patch adds two flush_tlb_mm() calls into
> sched.c on ia32 where there previously was no such call.

I thought I had a good reason. Let me check & make sure I didnt overlook
something. I'll get back to you.....

-- 
Thanks

Jack Steiner (steiner@sgi.com)          651-683-5302
Principal Engineer                      SGI - Silicon Graphics, Inc.