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

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

On Mon, Apr 13, 2015 at 04:11:19PM +0200, Laurent Dufour wrote:
> On 13/04/2015 16:02, Kirill A. Shutemov wrote:
> > On Mon, Apr 13, 2015 at 04:35:21PM +0300, Pavel Emelyanov wrote:
> >> On 04/13/2015 04:21 PM, Laurent Dufour wrote:
> >>> On 13/04/2015 15:13, Kirill A. Shutemov wrote:
> >>>> 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)
> >>>>
> >>>
> >>> I guessed you wanted the arch_remap() prototype to be exposed somewhere
> >>> in the code.
> >>>
> >>> To be honest, I can't find the benefit of defining a dummy arch_remap()
> >>> in mm/remap.c if __HAVE_ARCH_REMAP is not defined instead of calling it
> >>> in move_vma if __HAVE_ARCH_REMAP is defined.
> >>> Is it really what you want ?
> >>
> >> I think Kirill meant something like e.g. the arch_enter_lazy_mmu_mode()
> >> is implemented and called in mm/mremap.c -- the "generic" part is in the
> >> include/asm-generic/pgtable.h and those architectures willing to have
> >> their own implementation are in arch/$arch/...
> >>
> >> Kirill, if I'm right with it, can you suggest the header where to put
> >> the "generic" mremap hook's (empty) body?
> > 
> > I initially thought it would be enough to put it into
> > <asm-generic/mmu_context.h>, expecting it works as
> > <asm-generic/pgtable.h>. But that's not the case.
> > 
> > It probably worth at some point rework all <asm/mmu_context.h> to include
> > <asm-generic/mmu_context.h> at the end as we do for <asm/pgtable.h>.
> > But that's outside the scope of the patchset, I guess.
> > 
> > I don't see any better candidate for such dummy header. :-/
> 
> Clearly, I'm not confortable with a rewrite of <asm/mmu_context.h> :(
> 
> So what about this patch, is this v3 acceptable ?

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
 Kirill A. Shutemov