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Re: [PATCH v6v3 02/12] mm: migrate: support non-lru movable page migration

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  Re: [PATCH v6v3 02/12] mm: migrate: support non-lru movable page  migration Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-06-27 08:00 +0200
    Re: [PATCH v6v3 02/12] mm: migrate: support non-lru movable page  migration Minchan Kim <minchan@kernel.org> - 2016-06-28 08:40 +0200
      Re: [PATCH v6v3 02/12] mm: migrate: support non-lru movable page  migration Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-06-30 08:00 +0200
        Re: [PATCH v6v3 02/12] mm: migrate: support non-lru movable page  migration Minchan Kim <minchan@kernel.org> - 2016-06-30 08:20 +0200

#1431727 — Re: [PATCH v6v3 02/12] mm: migrate: support non-lru movable page migration

On 06/16/2016 11:07 AM, Minchan Kim wrote:
> On Thu, Jun 16, 2016 at 09:12:07AM +0530, Anshuman Khandual wrote:
>> On 06/16/2016 05:56 AM, Minchan Kim wrote:
>>> On Wed, Jun 15, 2016 at 12:15:04PM +0530, Anshuman Khandual wrote:
>>>> On 06/15/2016 08:02 AM, Minchan Kim wrote:
>>>>> Hi,
>>>>>
>>>>> On Mon, Jun 13, 2016 at 03:08:19PM +0530, Anshuman Khandual wrote:
>>>>>>> On 05/31/2016 05:31 AM, Minchan Kim wrote:
>>>>>>>>> @@ -791,6 +921,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
>>>>>>>>>  	int rc = -EAGAIN;
>>>>>>>>>  	int page_was_mapped = 0;
>>>>>>>>>  	struct anon_vma *anon_vma = NULL;
>>>>>>>>> +	bool is_lru = !__PageMovable(page);
>>>>>>>>>  
>>>>>>>>>  	if (!trylock_page(page)) {
>>>>>>>>>  		if (!force || mode == MIGRATE_ASYNC)
>>>>>>>>> @@ -871,6 +1002,11 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
>>>>>>>>>  		goto out_unlock_both;
>>>>>>>>>  	}
>>>>>>>>>  
>>>>>>>>> +	if (unlikely(!is_lru)) {
>>>>>>>>> +		rc = move_to_new_page(newpage, page, mode);
>>>>>>>>> +		goto out_unlock_both;
>>>>>>>>> +	}
>>>>>>>>> +
>>>>>>>
>>>>>>> Hello Minchan,
>>>>>>>
>>>>>>> I might be missing something here but does this implementation support the
>>>>>>> scenario where these non LRU pages owned by the driver mapped as PTE into
>>>>>>> process page table ? Because the "goto out_unlock_both" statement above
>>>>>>> skips all the PTE unmap, putting a migration PTE and removing the migration
>>>>>>> PTE steps.
>>>>> You're right. Unfortunately, it doesn't support right now but surely,
>>>>> it's my TODO after landing this work.
>>>>>
>>>>> Could you share your usecase?
>>>>
>>>> Sure.
>>>
>>> Thanks a lot!
>>>
>>>>
>>>> My driver has privately managed non LRU pages which gets mapped into user space
>>>> process page table through f_ops->mmap() and vmops->fault() which then updates
>>>> the file RMAP (page->mapping->i_mmap) through page_add_file_rmap(page). One thing
>>>
>>> Hmm, page_add_file_rmap is not exported function. How does your driver can use it?
>>
>> Its not using the function directly, I just re-iterated the sequence of functions
>> above. (do_set_pte -> page_add_file_rmap) gets called after we grab the page from
>> driver through (__do_fault->vma->vm_ops->fault()).
>>
>>> Do you use vm_insert_pfn?
>>> What type your vma is? VM_PFNMMAP or VM_MIXEDMAP?
>>
>> I dont use vm_insert_pfn(). Here is the sequence of events how the user space
>> VMA gets the non LRU pages from the driver.
>>
>> - Driver registers a character device with 'struct file_operations' binding
>> - Then the 'fops->mmap()' just binds the incoming 'struct vma' with a 'struct
>>   vm_operations_struct' which provides the 'vmops->fault()' routine which
>>   basically traps all page faults on the VMA and provides one page at a time
>>   through a driver specific allocation routine which hands over non LRU pages
>>
>> The VMA is not anything special as such. Its what we get when we try to do a
>> simple mmap() on a file descriptor pointing to a character device. I can
>> figure out all the VM_* flags it holds after creation.
>>
>>>
>>> I want to make dummy driver to simulate your case.
>>
>> Sure. I hope the above mentioned steps will help you but in case you need more
>> information, please do let me know.
> 
> I got understood now. :)
> I will test it with dummy driver and will Cc'ed when I send a patch.

Hello Minchan,

Do you have any updates on this ? The V7 of the series still has this limitation.
Did you get a chance to test the driver out ? I am still concerned about how to
handle the struct address_space override problem within the struct page.

- Anshuman

[toc] | [next] | [standalone]

#1432534

On Mon, Jun 27, 2016 at 11:21:01AM +0530, Anshuman Khandual wrote:
> On 06/16/2016 11:07 AM, Minchan Kim wrote:
> > On Thu, Jun 16, 2016 at 09:12:07AM +0530, Anshuman Khandual wrote:
> >> On 06/16/2016 05:56 AM, Minchan Kim wrote:
> >>> On Wed, Jun 15, 2016 at 12:15:04PM +0530, Anshuman Khandual wrote:
> >>>> On 06/15/2016 08:02 AM, Minchan Kim wrote:
> >>>>> Hi,
> >>>>>
> >>>>> On Mon, Jun 13, 2016 at 03:08:19PM +0530, Anshuman Khandual wrote:
> >>>>>>> On 05/31/2016 05:31 AM, Minchan Kim wrote:
> >>>>>>>>> @@ -791,6 +921,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> >>>>>>>>>  	int rc = -EAGAIN;
> >>>>>>>>>  	int page_was_mapped = 0;
> >>>>>>>>>  	struct anon_vma *anon_vma = NULL;
> >>>>>>>>> +	bool is_lru = !__PageMovable(page);
> >>>>>>>>>  
> >>>>>>>>>  	if (!trylock_page(page)) {
> >>>>>>>>>  		if (!force || mode == MIGRATE_ASYNC)
> >>>>>>>>> @@ -871,6 +1002,11 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> >>>>>>>>>  		goto out_unlock_both;
> >>>>>>>>>  	}
> >>>>>>>>>  
> >>>>>>>>> +	if (unlikely(!is_lru)) {
> >>>>>>>>> +		rc = move_to_new_page(newpage, page, mode);
> >>>>>>>>> +		goto out_unlock_both;
> >>>>>>>>> +	}
> >>>>>>>>> +
> >>>>>>>
> >>>>>>> Hello Minchan,
> >>>>>>>
> >>>>>>> I might be missing something here but does this implementation support the
> >>>>>>> scenario where these non LRU pages owned by the driver mapped as PTE into
> >>>>>>> process page table ? Because the "goto out_unlock_both" statement above
> >>>>>>> skips all the PTE unmap, putting a migration PTE and removing the migration
> >>>>>>> PTE steps.
> >>>>> You're right. Unfortunately, it doesn't support right now but surely,
> >>>>> it's my TODO after landing this work.
> >>>>>
> >>>>> Could you share your usecase?
> >>>>
> >>>> Sure.
> >>>
> >>> Thanks a lot!
> >>>
> >>>>
> >>>> My driver has privately managed non LRU pages which gets mapped into user space
> >>>> process page table through f_ops->mmap() and vmops->fault() which then updates
> >>>> the file RMAP (page->mapping->i_mmap) through page_add_file_rmap(page). One thing
> >>>
> >>> Hmm, page_add_file_rmap is not exported function. How does your driver can use it?
> >>
> >> Its not using the function directly, I just re-iterated the sequence of functions
> >> above. (do_set_pte -> page_add_file_rmap) gets called after we grab the page from
> >> driver through (__do_fault->vma->vm_ops->fault()).
> >>
> >>> Do you use vm_insert_pfn?
> >>> What type your vma is? VM_PFNMMAP or VM_MIXEDMAP?
> >>
> >> I dont use vm_insert_pfn(). Here is the sequence of events how the user space
> >> VMA gets the non LRU pages from the driver.
> >>
> >> - Driver registers a character device with 'struct file_operations' binding
> >> - Then the 'fops->mmap()' just binds the incoming 'struct vma' with a 'struct
> >>   vm_operations_struct' which provides the 'vmops->fault()' routine which
> >>   basically traps all page faults on the VMA and provides one page at a time
> >>   through a driver specific allocation routine which hands over non LRU pages
> >>
> >> The VMA is not anything special as such. Its what we get when we try to do a
> >> simple mmap() on a file descriptor pointing to a character device. I can
> >> figure out all the VM_* flags it holds after creation.
> >>
> >>>
> >>> I want to make dummy driver to simulate your case.
> >>
> >> Sure. I hope the above mentioned steps will help you but in case you need more
> >> information, please do let me know.
> > 
> > I got understood now. :)
> > I will test it with dummy driver and will Cc'ed when I send a patch.
> 
> Hello Minchan,
> 
> Do you have any updates on this ? The V7 of the series still has this limitation.
> Did you get a chance to test the driver out ? I am still concerned about how to
> handle the struct address_space override problem within the struct page.

Hi Anshuman,

Slow but I am working on that. :) However, as I said, I want to do it
after soft landing of current non-lru-no-mapped page migration to solve
current real field issues.

About the overriding problem of non-lru-mapped-page, I implemented dummy
driver as miscellaneous device and in test_mmap(file_operations.mmap),
I changed a_ops with my address_space_operations.

int test_mmap(struct file *filp, struct vm_area_struct *vma)
{
        filp->f_mapping->a_ops = &test_aops;
        vma->vm_ops = &test_vm_ops;
        vma->vm_private_data = filp->private_data;
        return 0;
}

test_aops should have *set_page_dirty* overriding.

static int test_set_pag_dirty(struct page *page)
{
        if (!PageDirty(page))
                SetPageDirty*page);
        return 0;
}

Otherwise, it goes BUG_ON during radix tree operation because
currently try_to_unmap is designed for file-lru pages which lives
in page cache so it propagates page table dirty bit to PG_dirty flag
of struct page by set_page_dirty. And set_page_dirty want to mark
dirty tag in radix tree node but it's character driver so the page
cache doesn't have it. That's why we encounter BUG_ON in radix tree
operation. Anyway, to test, I implemented set_page_dirty in my dummy
driver.

With only that, it doesn't work because I need to modify migrate.c to
work non-lru-mapped-page and changing PG_isolated flag which is
override of PG_reclaim which is cleared in set_page_dirty.

With that, it seems to work. But I'm not saying it's right model now
for device drivers. In runtime, replacing filp->f_mapping->a_ops with
custom a_ops of own driver seems to be hacky to me.
So, I'm considering now new pseudo fs "movable_inode" which will
support 

struct file *movable_inode_getfile(const char *name,
                        const struct file_operations *fop,
                        const struct address_space_operations *a_ops)
{
        struct path path;
        struct qstr this;
        struct inode *inode;
        struct super_block *sb;

        this.name = name;
        this.len = strlen(name);
        this.hash = 0;
        sb = movable_mnt.mnt_sb;
        patch.denty = d_alloc_pseudo(movable_inode_mnt->mnt_sb, &this);
        patch.mnt = mntget(movable_inode_mnt);
        
        inode = new_inode(sb);
        ..
        ..
        inode->i_mapping->a_ops = a_ops;
        d_instantiate(path.dentry, inode);

        return alloc_file(&path, FMODE_WRITE | FMODE_READ, f_op);
}

And in our driver, we can change vma->vm_file with new one.

int test_mmap(struct file *filp, struct vm_area_structd *vma)
{
        struct file *newfile = movable_inode_getfile("[test"],
                                filep->f_op, &test_aops);
        vma->vm_file = newfile;
        ..
        ..
}

When I read mmap_region in mm/mmap.c, it's reasonable usecase
which dirver's mmap changes vma->vm_file with own file.

Anyway, it needs many subtle changes in mm/vfs/driver side so
need to review from each maintainers related subsystem so I
want to not be hurry.

Thanks.

> 
> - Anshuman
> 

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#1434235

On 06/28/2016 12:09 PM, Minchan Kim wrote:
> On Mon, Jun 27, 2016 at 11:21:01AM +0530, Anshuman Khandual wrote:
>> On 06/16/2016 11:07 AM, Minchan Kim wrote:
>>> On Thu, Jun 16, 2016 at 09:12:07AM +0530, Anshuman Khandual wrote:
>>>> On 06/16/2016 05:56 AM, Minchan Kim wrote:
>>>>> On Wed, Jun 15, 2016 at 12:15:04PM +0530, Anshuman Khandual wrote:
>>>>>> On 06/15/2016 08:02 AM, Minchan Kim wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> On Mon, Jun 13, 2016 at 03:08:19PM +0530, Anshuman Khandual wrote:
>>>>>>>>> On 05/31/2016 05:31 AM, Minchan Kim wrote:
>>>>>>>>>>> @@ -791,6 +921,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
>>>>>>>>>>>  	int rc = -EAGAIN;
>>>>>>>>>>>  	int page_was_mapped = 0;
>>>>>>>>>>>  	struct anon_vma *anon_vma = NULL;
>>>>>>>>>>> +	bool is_lru = !__PageMovable(page);
>>>>>>>>>>>  
>>>>>>>>>>>  	if (!trylock_page(page)) {
>>>>>>>>>>>  		if (!force || mode == MIGRATE_ASYNC)
>>>>>>>>>>> @@ -871,6 +1002,11 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
>>>>>>>>>>>  		goto out_unlock_both;
>>>>>>>>>>>  	}
>>>>>>>>>>>  
>>>>>>>>>>> +	if (unlikely(!is_lru)) {
>>>>>>>>>>> +		rc = move_to_new_page(newpage, page, mode);
>>>>>>>>>>> +		goto out_unlock_both;
>>>>>>>>>>> +	}
>>>>>>>>>>> +
>>>>>>>>>
>>>>>>>>> Hello Minchan,
>>>>>>>>>
>>>>>>>>> I might be missing something here but does this implementation support the
>>>>>>>>> scenario where these non LRU pages owned by the driver mapped as PTE into
>>>>>>>>> process page table ? Because the "goto out_unlock_both" statement above
>>>>>>>>> skips all the PTE unmap, putting a migration PTE and removing the migration
>>>>>>>>> PTE steps.
>>>>>>> You're right. Unfortunately, it doesn't support right now but surely,
>>>>>>> it's my TODO after landing this work.
>>>>>>>
>>>>>>> Could you share your usecase?
>>>>>>
>>>>>> Sure.
>>>>>
>>>>> Thanks a lot!
>>>>>
>>>>>>
>>>>>> My driver has privately managed non LRU pages which gets mapped into user space
>>>>>> process page table through f_ops->mmap() and vmops->fault() which then updates
>>>>>> the file RMAP (page->mapping->i_mmap) through page_add_file_rmap(page). One thing
>>>>>
>>>>> Hmm, page_add_file_rmap is not exported function. How does your driver can use it?
>>>>
>>>> Its not using the function directly, I just re-iterated the sequence of functions
>>>> above. (do_set_pte -> page_add_file_rmap) gets called after we grab the page from
>>>> driver through (__do_fault->vma->vm_ops->fault()).
>>>>
>>>>> Do you use vm_insert_pfn?
>>>>> What type your vma is? VM_PFNMMAP or VM_MIXEDMAP?
>>>>
>>>> I dont use vm_insert_pfn(). Here is the sequence of events how the user space
>>>> VMA gets the non LRU pages from the driver.
>>>>
>>>> - Driver registers a character device with 'struct file_operations' binding
>>>> - Then the 'fops->mmap()' just binds the incoming 'struct vma' with a 'struct
>>>>   vm_operations_struct' which provides the 'vmops->fault()' routine which
>>>>   basically traps all page faults on the VMA and provides one page at a time
>>>>   through a driver specific allocation routine which hands over non LRU pages
>>>>
>>>> The VMA is not anything special as such. Its what we get when we try to do a
>>>> simple mmap() on a file descriptor pointing to a character device. I can
>>>> figure out all the VM_* flags it holds after creation.
>>>>
>>>>>
>>>>> I want to make dummy driver to simulate your case.
>>>>
>>>> Sure. I hope the above mentioned steps will help you but in case you need more
>>>> information, please do let me know.
>>>
>>> I got understood now. :)
>>> I will test it with dummy driver and will Cc'ed when I send a patch.
>>
>> Hello Minchan,
>>
>> Do you have any updates on this ? The V7 of the series still has this limitation.
>> Did you get a chance to test the driver out ? I am still concerned about how to
>> handle the struct address_space override problem within the struct page.
> 
> Hi Anshuman,
> 
> Slow but I am working on that. :) However, as I said, I want to do it

I really appreciate. Was just curious about the problem and any potential
solution we can look into.

> after soft landing of current non-lru-no-mapped page migration to solve
> current real field issues.

yeah it makes sense.

> 
> About the overriding problem of non-lru-mapped-page, I implemented dummy
> driver as miscellaneous device and in test_mmap(file_operations.mmap),
> I changed a_ops with my address_space_operations.
> 
> int test_mmap(struct file *filp, struct vm_area_struct *vma)
> {
>         filp->f_mapping->a_ops = &test_aops;
>         vma->vm_ops = &test_vm_ops;
>         vma->vm_private_data = filp->private_data;
>         return 0;
> }
> 

Okay.

> test_aops should have *set_page_dirty* overriding.
> 
> static int test_set_pag_dirty(struct page *page)
> {
>         if (!PageDirty(page))
>                 SetPageDirty*page);
>         return 0;
> }
> 
> Otherwise, it goes BUG_ON during radix tree operation because
> currently try_to_unmap is designed for file-lru pages which lives
> in page cache so it propagates page table dirty bit to PG_dirty flag
> of struct page by set_page_dirty. And set_page_dirty want to mark
> dirty tag in radix tree node but it's character driver so the page
> cache doesn't have it. That's why we encounter BUG_ON in radix tree
> operation. Anyway, to test, I implemented set_page_dirty in my dummy
> driver.

Okay and the above test_set_page_dirty() example is sufficient ?

> 
> With only that, it doesn't work because I need to modify migrate.c to
> work non-lru-mapped-page and changing PG_isolated flag which is
> override of PG_reclaim which is cleared in set_page_dirty.

Got it, so what changes you did ? Implemented PG_isolated differently
not by overriding PG_reclaim or something else ? Yes set_page_dirty
indeed clears the PG_reclaim flag.

> 
> With that, it seems to work. But I'm not saying it's right model now

So the mapped pages migration was successful ? Even after overloading
filp->f_mapping->a_ops = &test_aops, we still have the RMAP information
intact with filp->f_mappinp pointed interval tree. But would really like
to see the code changes.

> for device drivers. In runtime, replacing filp->f_mapping->a_ops with
> custom a_ops of own driver seems to be hacky to me.

Yeah I thought so.

> So, I'm considering now new pseudo fs "movable_inode" which will
> support 
> 
> struct file *movable_inode_getfile(const char *name,
>                         const struct file_operations *fop,
>                         const struct address_space_operations *a_ops)
> {
>         struct path path;
>         struct qstr this;
>         struct inode *inode;
>         struct super_block *sb;
> 
>         this.name = name;
>         this.len = strlen(name);
>         this.hash = 0;
>         sb = movable_mnt.mnt_sb;
>         patch.denty = d_alloc_pseudo(movable_inode_mnt->mnt_sb, &this);
>         patch.mnt = mntget(movable_inode_mnt);
>         
>         inode = new_inode(sb);
>         ..
>         ..
>         inode->i_mapping->a_ops = a_ops;
>         d_instantiate(path.dentry, inode);
> 
>         return alloc_file(&path, FMODE_WRITE | FMODE_READ, f_op);
> }
> 
> And in our driver, we can change vma->vm_file with new one.
> 
> int test_mmap(struct file *filp, struct vm_area_structd *vma)
> {
>         struct file *newfile = movable_inode_getfile("[test"],
>                                 filep->f_op, &test_aops);
>         vma->vm_file = newfile;
>         ..
>         ..
> }
> 
> When I read mmap_region in mm/mmap.c, it's reasonable usecase
> which dirver's mmap changes vma->vm_file with own file.

I will look into these details.

> Anyway, it needs many subtle changes in mm/vfs/driver side so
> need to review from each maintainers related subsystem so I
> want to not be hurry.

Sure, makes sense. Mean while it will be really great if you could share
your code changes as described above, so that I can try them out.

[toc] | [prev] | [next] | [standalone]

#1434240

On Thu, Jun 30, 2016 at 11:26:45AM +0530, Anshuman Khandual wrote:

<snip>

> >> Did you get a chance to test the driver out ? I am still concerned about how to
> >> handle the struct address_space override problem within the struct page.
> > 
> > Hi Anshuman,
> > 
> > Slow but I am working on that. :) However, as I said, I want to do it
> 
> I really appreciate. Was just curious about the problem and any potential
> solution we can look into.
> 
> > after soft landing of current non-lru-no-mapped page migration to solve
> > current real field issues.
> 
> yeah it makes sense.
> 
> > 
> > About the overriding problem of non-lru-mapped-page, I implemented dummy
> > driver as miscellaneous device and in test_mmap(file_operations.mmap),
> > I changed a_ops with my address_space_operations.
> > 
> > int test_mmap(struct file *filp, struct vm_area_struct *vma)
> > {
> >         filp->f_mapping->a_ops = &test_aops;
> >         vma->vm_ops = &test_vm_ops;
> >         vma->vm_private_data = filp->private_data;
> >         return 0;
> > }
> > 
> 
> Okay.
> 
> > test_aops should have *set_page_dirty* overriding.
> > 
> > static int test_set_pag_dirty(struct page *page)
> > {
> >         if (!PageDirty(page))
> >                 SetPageDirty*page);
> >         return 0;
> > }
> > 
> > Otherwise, it goes BUG_ON during radix tree operation because
> > currently try_to_unmap is designed for file-lru pages which lives
> > in page cache so it propagates page table dirty bit to PG_dirty flag
> > of struct page by set_page_dirty. And set_page_dirty want to mark
> > dirty tag in radix tree node but it's character driver so the page
> > cache doesn't have it. That's why we encounter BUG_ON in radix tree
> > operation. Anyway, to test, I implemented set_page_dirty in my dummy
> > driver.
> 
> Okay and the above test_set_page_dirty() example is sufficient ?

I guess just return 0 is sufficeint without any dirting a page.

> 
> > 
> > With only that, it doesn't work because I need to modify migrate.c to
> > work non-lru-mapped-page and changing PG_isolated flag which is
> > override of PG_reclaim which is cleared in set_page_dirty.
> 
> Got it, so what changes you did ? Implemented PG_isolated differently
> not by overriding PG_reclaim or something else ? Yes set_page_dirty
> indeed clears the PG_reclaim flag.
> 
> > 
> > With that, it seems to work. But I'm not saying it's right model now
> 
> So the mapped pages migration was successful ? Even after overloading
> filp->f_mapping->a_ops = &test_aops, we still have the RMAP information
> intact with filp->f_mappinp pointed interval tree. But would really like
> to see the code changes.
> 
> > for device drivers. In runtime, replacing filp->f_mapping->a_ops with
> > custom a_ops of own driver seems to be hacky to me.
> 
> Yeah I thought so.
> 
> > So, I'm considering now new pseudo fs "movable_inode" which will
> > support 
> > 
> > struct file *movable_inode_getfile(const char *name,
> >                         const struct file_operations *fop,
> >                         const struct address_space_operations *a_ops)
> > {
> >         struct path path;
> >         struct qstr this;
> >         struct inode *inode;
> >         struct super_block *sb;
> > 
> >         this.name = name;
> >         this.len = strlen(name);
> >         this.hash = 0;
> >         sb = movable_mnt.mnt_sb;
> >         patch.denty = d_alloc_pseudo(movable_inode_mnt->mnt_sb, &this);
> >         patch.mnt = mntget(movable_inode_mnt);
> >         
> >         inode = new_inode(sb);
> >         ..
> >         ..
> >         inode->i_mapping->a_ops = a_ops;
> >         d_instantiate(path.dentry, inode);
> > 
> >         return alloc_file(&path, FMODE_WRITE | FMODE_READ, f_op);
> > }
> > 
> > And in our driver, we can change vma->vm_file with new one.
> > 
> > int test_mmap(struct file *filp, struct vm_area_structd *vma)
> > {
> >         struct file *newfile = movable_inode_getfile("[test"],
> >                                 filep->f_op, &test_aops);
> >         vma->vm_file = newfile;
> >         ..
> >         ..
> > }
> > 
> > When I read mmap_region in mm/mmap.c, it's reasonable usecase
> > which dirver's mmap changes vma->vm_file with own file.
> 
> I will look into these details.
> 
> > Anyway, it needs many subtle changes in mm/vfs/driver side so
> > need to review from each maintainers related subsystem so I
> > want to not be hurry.
> 
> Sure, makes sense. Mean while it will be really great if you could share
> your code changes as described above, so that I can try them out.
> 

It's almost done for draft version and I'm doing stress test now and
fortunately, doesn't see the problem until now.

I will send you when I'm ready.

Thanks.

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