On Thu, Mar 21, 2013 at 04:32:03PM +0800, Simon Jeons wrote: >Hi Michal, >On 03/21/2013 04:19 PM, Michal Hocko wrote: >>On Thu 21-03-13 10:33:07, Simon Jeons wrote: >>>Hi Mel, >>>On 03/21/2013 02:19 AM, Mel Gorman wrote: >>>>The following problem was reported against a distribution kernel when >>>>zone_reclaim was enabled but the same problem applies to the mainline >>>>kernel. The reproduction case was as follows >>>> >>>>1. Run numactl -m +0 dd if=largefile of=/dev/null >>>> This allocates a large number of clean pages in node 0 >>>I confuse why this need allocate a large number of clean pages? >>It reads from file and puts pages into the page cache. The pages are not >>modified so they are clean. Output file is /dev/null so no pages are >>written. dd doesn't call fadvise(POSIX_FADV_DONTNEED) on the input file >>by default so pages from the file stay in the page cache > >Thanks for your clarify Michal. >dd will use page cache instead of direct IO? Where can I got dd >source codes? >One offline question, when should use page cache and when should use >direct IO? who prefer direct IO: - the users believe they can manage caching of file contents better than the kernel can. - the users want to avoid overflowing the page cache with data which is unlikely to be of use in the near future. Regards, Wanpeng Li > > >-- >To unsubscribe, send a message with 'unsubscribe linux-mm' in >the body to majordomo@xxxxxxxxx. For more info on Linux MM, >see: http://www.linux-mm.org/ . >Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>