William Lee Irwin III wrote:

quoted

SetPageFreeing is only done in shrink_list(), so other pages in the
buddy bitmaps and/or pagecache pages freed by other methods may not

On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote:

It is also done by remove_exclusive_swap_page, although that hunk
leaked into a later patch (#5), sorry.
Other methods (eg truncate) don't seem to have an atomicity guarantee
anyway - ie. it is valid to pick up a reference on a page that is
just about to get truncated. PageFreeing is only used when some code
is making an assumption about the number of users of the page.

tmpfs


William Lee Irwin III wrote:

quoted

be found by this. There's also likely trouble with higher-order pages.

On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote:

There isn't because higher order pages aren't used for pagecache.

hugetlbfs


William Lee Irwin III wrote:

quoted

page != *pagep won't be reliably tripped unless the pagecache
modification has the appropriate memory barriers.

On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote:

There are appropriate memory barriers: the radix tree is
modified uner the rwlock/spinlock, and this function has
a memory barrier before testing page != *pagep.

Someone else deal with this (paulus? anton? other arch maintainers?).


William Lee Irwin III wrote:

quoted

The lockless radix tree lookups are a harder problem than this, and
the implementation didn't look promising. I have other problems to deal
with so I'm not going to go very far into this.

On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote:

What's wrong with the lockless radix tree lookups?

The above is as much as I wanted to go into it. I need to direct my
capacity for the grunt work of devising adversary arguments elsewhere.


William Lee Irwin III wrote:

quoted

While I agree that locklessness is the right direction for the
pagecache to go, this RFC seems to have too far to go to use it to
conclude anything about the subject.

On Tue, Jun 28, 2005 at 10:03:00AM +1000, Nick Piggin wrote:

You don't seem to have looked enough to conclude anything about it.

You requested comments. I made some.

Anyhow, my review has not been comprehensive. I stopped after the first
few things I found that needed fixing. If others could deal with the
rest of this, I'd be much obliged.


-- wli
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