Hi Trond, On Wed, 2012-02-08 at 04:55 +0000, Myklebust, Trond wrote: > Applications that need to use uncached i/o are required to use the > O_DIRECT open() mode instead, since pretty much all of them need to be > rewritten to deal with the subtleties involved anyway. Could you please expand on the subtleties involved that require an application to be rewritten if forcedirectio mount option was available? A scenario where forcedirectio would be useful is when an application reads nearly a TB of data from local disks, processes that data and then dumps it to an NFS mount. All that happens while other processes are reading/writing to the local disks. The application does not have an O_DIRECT option nor is the source code available. With paged I/O the problem we see is that the NFS client system reaches dirty_bytes/dirty_ratio threshold and then blocks/forces all the processes to flush dirty pages. This effectively 'locks' up the NFS client system while the NFS dirty pages are pushed slowly over the wire to the NFS server. Some of the processes that have nothing to do with writing to the NFS mount are badly impacted. A forcedirectio mount option would be very helpful in this scenario. Do you have any advice on alleviating such problems on the NFS client by only using existing tunables? Thanks, # -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
