On 6/12/2013 3:26 AM, Roger Oberholtzer wrote: ... > I have an application that is streaming data to an XFS disk at a > sustained 25 MB/sec. This is well below what the hardware supports. The > application does fopen/fwrite/fclose (no active flushing or syncing). Buffered IO. > I see that as my application writes data (the only process writing the > only open file on the disk), the system cache grows and grows. Here is > the unusual part: periodically, writes take some number of seconds to > complete, rather than the typical <50 msecs). The increased time seems > to correspond to the increasing size of the page cache. Standard Linux buffered IO behavior. Note this is not XFS specific. > If I do: > > echo 1 > /proc/sys/vm/drop_caches Dumps the page cache forcing your buffered writes to disk. > while the application is runnung, then the writes do not occasionally > take longer. Until the cache grows again, and I do the echo again. Which seems a bit laborious. > I am sure I must be misinterpreting what I see. Nope. The Linux virtual memory system has behaved this way for quite some time. You can teak how long IOs stay in cache. See dirty_* at https://www.kernel.org/doc/Documentation/sysctl/vm.txt Given the streaming nature you describe, have you looked at possibly using O_DIRECT? -- Stan _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
