Messages in this thread | | | Date | Thu, 21 Mar 2013 16:32:03 +0800 | From | Simon Jeons <> | Subject | Re: [PATCH] mm: page_alloc: Avoid marking zones full prematurely after zone_reclaim() |
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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?
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