Re: [patch] mm: bug in set_page_dirty_buffers

[Nick Piggin <npiggin@suse.de>]

On Tue, Oct 10, 2006 at 09:11:03AM +0200, Peter Zijlstra wrote:
> On Tue, 2006-10-10 at 08:59 +0200, Nick Piggin wrote:
> > 
> > What's your problem with zap_pte_range?
> 
> well, not only zap_pte_range, also page_remove_rmap and
> try_to_unmap_cluster etc.. Basically all those who fiddle with the page
> without holding the page lock.

Fiddle with the page -- as in setting it dirty? Because there is a
huge amount of other stuff that fiddles with the page without taking
the lock ;)

> Because with concurrent pagecache, there is no tree lock anymore to
> protect/pin the whole mapping, I need to go pin individual pages.
> Perhaps having an inner page bit-spinlock (PG_pin) isn't a bad thing,
> I'd just raised the issue to see if it would be doable/a-good-thing to
> try and merge these two.

It does seem attractive, but at the moment I can't see how it would
be done. One of the main problems is that truncate / invalidate need
to hold the page locked while traversing the rmaps (which require
i_mmap_lock, ptl locks, etc).

There are other things too, like the swapcache, which uses PG_locked
as an outer lock.

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