Subject: Re: [RESEND PATCH v3 1/2] mm: Introducing arch_remap hook

From: Laurent Dufour <[email-masked]>
Date: Mon, 13 Apr 2015 14:41:22 +0200

On 13/04/2015 13:58, Kirill A. Shutemov wrote:
> On Mon, Apr 13, 2015 at 11:56:27AM +0200, Laurent Dufour wrote:
>> Some architecture would like to be triggered when a memory area is moved
>> through the mremap system call.
>>
>> This patch is introducing a new arch_remap mm hook which is placed in the
>> path of mremap, and is called before the old area is unmapped (and the
>> arch_unmap hook is called).
>>
>> The architectures which need to call this hook should define
>> __HAVE_ARCH_REMAP in their asm/mmu_context.h and provide the arch_remap
>> service with the following prototype:
>> void arch_remap(struct mm_struct *mm,
>>                 unsigned long old_start, unsigned long old_end,
>>                 unsigned long new_start, unsigned long new_end);
>>
>> Signed-off-by: Laurent Dufour <[email-masked]>
>> Reviewed-by: Ingo Molnar <[email-masked]>
>> ---
>>  mm/mremap.c | 19 +++++++++++++------
>>  1 file changed, 13 insertions(+), 6 deletions(-)
>>
>> diff --git a/mm/mremap.c b/mm/mremap.c
>> index 2dc44b1cb1df..009db5565893 100644
>> --- a/mm/mremap.c
>> +++ b/mm/mremap.c
>> @@ -25,6 +25,7 @@
>>  
>>  #include <asm/cacheflush.h>
>>  #include <asm/tlbflush.h>
>> +#include <asm/mmu_context.h>
>>  
>>  #include "internal.h"
>>  
>> @@ -286,13 +287,19 @@ static unsigned long move_vma(struct vm_area_struct *vma,
>>  		old_len = new_len;
>>  		old_addr = new_addr;
>>  		new_addr = -ENOMEM;
>> -	} else if (vma->vm_file && vma->vm_file->f_op->mremap) {
>> -		err = vma->vm_file->f_op->mremap(vma->vm_file, new_vma);
>> -		if (err < 0) {
>> -			move_page_tables(new_vma, new_addr, vma, old_addr,
>> -					 moved_len, true);
>> -			return err;
>> +	} else {
>> +		if (vma->vm_file && vma->vm_file->f_op->mremap) {
>> +			err = vma->vm_file->f_op->mremap(vma->vm_file, new_vma);
>> +			if (err < 0) {
>> +				move_page_tables(new_vma, new_addr, vma,
>> +						  old_addr, moved_len, true);
>> +				return err;
>> +			}
>>  		}
>> +#ifdef __HAVE_ARCH_REMAP
> 
> It would be cleaner to provide dummy arch_remap() for !__HAVE_ARCH_REMAP
> in some generic header.

The idea was to not impact all the architectures as arch_unmap(),
arch_dup_mmap() or arch_exit_mmap() implies.

I look at the headers where such a dummy arch_remap could be put but I
can't figure out one which will not impact all the architecture.
What about defining a dummy service earlier in mm/remap.c in the case
__HAVE_ARCH_REMAP is not defined ?
Something like :
#ifndef __HAVE_ARCH_REMAP
static inline void void arch_remap(struct mm_struct *mm,
                                   unsigned long old_start,
                                   unsigned long old_end,
                                   unsigned long new_start,
                                   unsigned long new_end)
{
}
#endif

> 
> 
>> +		arch_remap(mm, old_addr, old_addr+old_len,
>> +			   new_addr, new_addr+new_len);
> 
> Spaces around '+'?

Nice catch ;)

Thanks,
Laurent.

> 
>> +#endif
>>  	}
>>  
>>  	/* Conceal VM_ACCOUNT so old reservation is not undone */
>> -- 
>> 1.9.1
>>
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>