Messages in this thread | | | Date | Wed, 7 Oct 2009 12:48:31 +0900 | Subject | Re: [PATCH 2/2] mlock use lru_add_drain_all_async() | From | KOSAKI Motohiro <> |
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Hi
> Hello KOSAKI-san, > > Few questions on the lru_add_drain_all_async(). If i understand > correctly, the reason that we have lru_add_drain_all() in the mlock() > call is to isolate mlocked pages into the separate LRU in case they > are sitting in pagevec. > > And I also understand the RT use cases you put in the patch > description, now my questions is that do we have race after applying > the patch? For example that if the RT task not giving up the cpu by > the time mlock returns, you have pages left in the pagevec which not > being drained back to the lru list. Do we have problem with that?
This patch don't introduce new race. current code has following race.
1. call mlock 2. lru_add_drain_all() 3. another cpu grab the page into its pagevec 4. actual PG_mlocked processing
I'd like to explain why this code works. linux has VM_LOCKED in vma and PG_mlocked in page. if we failed to turn on PG_mlocked, we can recover it at vmscan phase by VM_LOCKED.
Then, this patch effect are - increase race possibility a bit - decrease RT-task problem risk
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