On Tue, 8 Jun 2010 10:02:25 +0100 Mel Gorman <mel@xxxxxxxxx> wrote: > When memory is under enough pressure, a process may enter direct > reclaim to free pages in the same manner kswapd does. If a dirty page is > encountered during the scan, this page is written to backing storage using > mapping->writepage. This can result in very deep call stacks, particularly > if the target storage or filesystem are complex. It has already been observed > on XFS that the stack overflows but the problem is not XFS-specific. > > This patch prevents direct reclaim writing back pages by not setting > may_writepage in scan_control. Instead, dirty pages are placed back on the > LRU lists for either background writing by the BDI threads or kswapd. If > in direct lumpy reclaim and dirty pages are encountered, the process will > kick the background flushter threads before trying again. > This wouldn't have worked at all well back in the days when you could dirty all memory with MAP_SHARED. The balance_dirty_pages() calls on the fault path will now save us but if for some reason we were ever to revert those, we'd need to revert this change too, I suspect. As it stands, it would be wildly incautious to make a change like this without first working out why we're pulling so many dirty pages off the LRU tail, and fixing that. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
