Re: [PATCH] update ctime and mtime for mmaped write

[Peter Staubach <staubach@redhat.com>]

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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