> >>> 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()?
That's basically just an optimization. If it wasn't there, then data
from a another (shared) mapping could be written back, which is not
wrong, but not required either.
> 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.
The problems will start, when you have a file that is both mapped and
modified with write(). Then the dirying from the write() will set the
flag, and that will have undesirable consequences.
Miklos
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