Re: [PATCH] memory mapped files not updating timestamps

From: Peter Zijlstra
Date: Thu May 18 2006 - 06:57:41 EST

On Wed, 2006-05-17 at 20:24 +0100, Hugh Dickins wrote:
> On Wed, 17 May 2006, Peter Staubach wrote:

> > The changes add support to detect when the modification time needs to be
> > updated by placing a hook in __set_pages_dirty_buffers and
> > __set_pages_dirty_nobuffers. One of these two routines will be invoked
> > when the dirty bit is detected in the pte. The hook sets a new bit in the
> > address_space mapping struct indicating that the file which is associated
> > with that part of the address space needs to have its modification and
> > change time attributes updated.
> You're adding a little overhead to every set_page_dirty, when the vast
> majority (ordinary writes) don't need it: their mctime update is already
> well taken care of. (Or should we be deleting the code that does that?
> I think I'd rather not dare.)

It would make the code more symetric.

> I think you'd do better to target those places where set_page_dirty is
> called on a mapped page - and do the file_update_time at that point -
> or as near to that point as is sensible/permitted given the locking
> (vma->vm_file gives you the file without needing inode_update_time).

> Peter Zijlstra has patches relating to dirty mmaps in the -mm tree
> at present: I need to take a look at those, and I'll see if it would
> make sense to factor in this mctime issue on top of those - you may
> want to do the same.

Look for the callsites of set_page_dirty_balance(), those two points are
where writable file pages are dirtied.


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