On 01/15/2014 12:47 AM, Trond Myklebust wrote: > > 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. OK I'll try that. Thanks Boaz -- 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
