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

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Date:	Wed, 21 Feb 2007 19:23:29 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	staubach@...hat.com
CC:	akpm@...ux-foundation.org, hugh@...itas.com,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] update ctime and mtime for mmaped write

> > 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.

> > +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.

Thanks,
Miklos
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