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SubjectRe: [PATCH] update ctime and mtime for mmaped write
Miklos Szeredi wrote:
>>> Inspired by Peter Staubach's patch and the resulting comments.
>>>
>>>
>>>
>> An updated version of the original patch was submitted to LKML
>> yesterday... :-)
>>
>
> Strange coincidence :)
>
>
>>> file = vma->vm_file;
>>> start = vma->vm_end;
>>> + mapping_update_time(file);
>>> if ((flags & MS_SYNC) && file &&
>>> (vma->vm_flags & VM_SHARED)) {
>>> get_file(file);
>>>
>>>
>> It seems to me that this might lead to file times being updated for
>> non-MAP_SHARED mappings.
>>
>
> In theory no, because the COW-ed pages become anonymous and are not
> part of the original mapping any more.
>
>

I must profess to having a incomplete understanding of all of this
support, but then why would it be necessary to test VM_SHARED at
this point in msync()?

I ran into problems early on with file times being updated incorrectly
so I am a little sensitive this aspect.

>>> +int set_page_dirty_mapping(struct page *page);
>>>
>>>
>> This aspect of the design seems intrusive to me. I didn't see a strong
>> reason to introduce new versions of many of the routines just to handle
>> these semantics. What motivated this part of your design? Why the new
>> _mapping versions of routines?
>>
>
> Because there's no way to know inside the set_page_dirty() functions
> if the dirtying comes from a memory mapping or from a modification
> through a normal write(). And they have different semantics, for
> write() the modification times are updated immediately.

Perhaps I didn't understand what page_mapped() does, but it does seem to
have the right semantics as far as I could see.

Thanx...

ps
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