On Jan 14, 2014, at 17:43, Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> wrote: > > On Jan 14, 2014, at 17:21, Boaz Harrosh <bharrosh@xxxxxxxxxxx> wrote: > >> On 01/14/2014 09:05 PM, Trond Myklebust wrote: >>> On Tue, 2014-01-14 at 17:32 +0200, Boaz Harrosh wrote: >>>> >>> >>> For the default mount option of 'timeo=600', and the default #define >>> NFS4_POLL_RETRY_MIN==HZ/10, this means we can end up pounding the server >>> with 600 LAYOUTGET requests within the space of 1 minute, before giving >>> up. Is that reasonable? >>> >> >> It will never get there it will always be 1 or two sends. Usually it is >> just so the sequence of layout_get_done is out of the way and the >> LAYOUT_RECALL sequence+1 can get through and the layout released. Then >> the next time it will all be good and the LAYOUT_GET will succeed. >> >> Worst case is when the client is very busy with queue full of IO >> on the same busy layout that needs to be released by the recall. Personally >> I found that this never exceeds 40 IOPs in flight. Note that this is not >> the amount of total dirty memory but only the amount of already submitted >> IO. I guess that on a very slow connection these can take time but in >> regular line speeds I never observed more the 2 retries with this patch. >> >> It is all up to the client. NFS4ERR_RECALLCONFLICT means "the layouts you >> have need to be released" (I say released because the forgetful model does >> not actually returns them). Can you see a critical time when layouts are >> held for longer than a second ? > > That will probably depend on the workload and possibly on the layout type. > > My point was, however, about the potential for mischief due to the mismatch between the number of retries that the resulting code allows, and the fixed period between those retries of 1/10 seconds. Why not rather use something along the lines of "rpc_delay(rpc_task, min(giveup -jiffies , max(jiffies - lgp->args.timestamp, NFS4_POLL_RETRY_MIN)));”? That gives you an initially exponential back off with a minimum period of NFS4_POLL_RETRY_MIN, and with an expiry date of ‘timeo’ jiffies after the first attempt. Whoops. That should probably be max(NFS4_POLL_RETRY_MIN, min(giveup - jiffies , jiffies - lgp->args.timestamp)) so that the time interval is not < NFS4_POLL_RETRY_MIN. -- Trond Myklebust Linux NFS client maintainer -- 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
