Re: [PATCH] Scalable page cache

[Ingo Molnar]

hm, as far as i can see, your patch dirties both cachelines of the target
struct page on every lookup (page_splay_tree_find()), correct? If correct,
is this just an implementational thing, or something more fundamental?

i've been thinking about getting rid of some of the cacheline dirtying in
the page lookup code, ie. something like this:

- #define SetPageReferenced(page)    set_bit(PG_referenced, &(page)->flags)
+ #define SetPageReferenced(page) \
+	if (!test_bit(PG_referenced), &(page)->flags) \
+		set_bit(PG_referenced, &(page)->flags)

this would have the benefit of not touching the cacheline while doing a
simple read(), if the referenced bit is still set. (which is not cleared
too eagerly in most no-VM-pressure cases.) And it should not be a problem
that this is not race-free - missing to set the referenced bit is not a
big failure.

	Ingo