Return-Path: linux-nfs-owner@vger.kernel.org Received: from natasha.panasas.com ([209.166.131.148]:41034 "EHLO natasha.panasas.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751918AbaANXmH (ORCPT ); Tue, 14 Jan 2014 18:42:07 -0500 Message-ID: <52D5CB44.6080605@panasas.com> Date: Wed, 15 Jan 2014 01:41:56 +0200 From: Boaz Harrosh MIME-Version: 1.0 To: Trond Myklebust CC: NFS list , Stable Tree Subject: Re: [PATCH v2] pnfs: Proper delay for NFS4ERR_RECALLCONFLICT in layout_get_done References: <52D5589A.7090507@panasas.com> <1389726356.6420.5.camel@leira.trondhjem.org> <52D5B886.6000803@panasas.com> <42EE44E9-1051-4D22-A4B6-D7E70A59ED2D@primarydata.com> <153DAED6-461B-43A4-A5B2-A79C8E893285@primarydata.com> In-Reply-To: <153DAED6-461B-43A4-A5B2-A79C8E893285@primarydata.com> Content-Type: text/plain; charset="UTF-8" Sender: linux-nfs-owner@vger.kernel.org List-ID: On 01/15/2014 12:47 AM, Trond Myklebust wrote: > > On Jan 14, 2014, at 17:43, Trond Myklebust wrote: > >> >> On Jan 14, 2014, at 17:21, Boaz Harrosh 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