On 07/19/2010 09:11 AM, Mel Gorman 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 filesystem pages by checking if current is kswapd or the page is anonymous before writing back. If the dirty pages cannot be written back, they 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 stall for the background flusher before trying to reclaim the pages again. As the call-chain for writing anonymous pages is not expected to be deep and they are not cleaned by flusher threads, anonymous pages are still written back in direct reclaim. Signed-off-by: Mel Gorman<mel@xxxxxxxxx>
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