On Thu, Apr 08, 2010 at 07:58:47PM +0200, Andrea Arcangeli wrote:
> On Thu, Apr 08, 2010 at 07:56:04PM +0200, Johannes Weiner wrote:
> > Humm, maybe the start pfn could be huge page aligned? That would make
> > it possible to check for PageTransHuge() and skip over compound_order()
> > pages. This way, we should never actually run into PG_tail pages.
>
> The problem here are random compound pages that aren't owned by the
> transparent hugepage subsystem. If we can't identify those, it's
> unsafe to call compound_order (like it's unsafe to call page_order for
> pagebuddy pages).
But transparent huge pages are the only compound pages on the LRU, so
we should be able to identify them.
The lru_lock excludes isolation, splitting and collapsing, so I think
this is safe:
if (PageLRU() && PageTransCompound()) {
low_pfn += (1 << compound_order()) - 1
continue
}
if (__isolate_lru_page())
continue
...
Do I still miss something? If so, I will shut up now :-)
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