Messages in this thread |  | | | Subject | Re: [patch v2] vmscan: protect zone rotation stats by lru lock | | From | Lee Schermerhorn <> | | Date | Mon, 01 Dec 2008 17:09:45 -0500 |
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On Mon, 2008-12-01 at 16:46 -0500, Rik van Riel wrote: > 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.
And he's not actually adding a lock. Just moving the exiting one up to include the stats update. The intervening pagevec, pgmoved and lru initializations don't need to be under the lock, but that's probably not a big deal?
Lee
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