Messages in this thread | | | Date | Mon, 01 Dec 2008 16:46:35 -0500 | From | Rik van Riel <> | Subject | Re: [patch v2] vmscan: protect zone rotation stats by lru lock |
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Andrew Morton wrote: > On Mon, 01 Dec 2008 03:00:35 +0100 > Johannes Weiner <hannes@saeurebad.de> wrote: > >> The zone's rotation statistics must not be accessed without the >> corresponding LRU lock held. Fix an unprotected write in >> shrink_active_list(). >> > > I don't think it really matters. It's quite common in that code to do > unlocked, racy update to statistics such as this. Because on those > rare occasions where a race does happen, there's a small glitch in the > reclaim logic which nobody will notice anyway. > > Of course, this does need to be done with some care, to ensure the > glitch _will_ be small.
Processing at most SWAP_CLUSTER_MAX pages at once probably ensures that glitches will be small most of the time.
The only way this could be a big problem is if we end up racing with the divide-by-two logic in get_scan_ratio, leaving the rotated pages a factor two higher than they should be.
Putting all the writes to the stats under the LRU lock should ensure that never happens.
-- All rights reversed.
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