Re: Race in new page migration code?

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Christoph Lameter wrote:
On Sat, 14 Jan 2006, Nick Piggin wrote:


We take that reference count on the page:

Yes, after you have dropped all your claims to pin this page
(ie. pte lock). You really can't take a refcount on a page that


Oh. Now I see. I screwed that up by a fix I added.... We cannot drop the ptl here. So back to the way it was before. Remove the draining from isolate_lru_page and do it before scanning for pages so that we do not have to drop the ptl.

OK (either way is fine), but you should still drop the __isolate_lru_page
nonsense and revert it like my patch does.

Also remove the WARN_ON since its now even possible that other actions of the VM move the pages into the LRU lists while we scan for pages to
migrate.


Well, it has always been possible since vmscan started batching scans a
long time ago. Actually seeing as you only take a read lock on the semaphore
it is probably also possible to have a concurrent migrate operation cause
this as well.

Thanks,
Nick

--
SUSE Labs, Novell Inc.

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