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

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Mon, Apr 13, 2015 at 02:41:22PM +0200, Laurent Dufour wrote:
> 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 <ldufour@linux.vnet.ibm.com>
> >> Reviewed-by: Ingo Molnar <mingo@kernel.org>
> >> ---
> >>  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

Or just #define arch_remap(...) do { } while (0)

-- 
 Kirill A. Shutemov

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