On Sat, Jun 11, 2011 at 7:20 AM, Boaz Harrosh <bharrosh@xxxxxxxxxxx> wrote: > On 06/10/2011 12:23 PM, Benny Halevy wrote: >> On 2011-06-10 10:09, tao.peng@xxxxxxx wrote: >> >> A simple algorithm I can suggest is: >> - on initialization, calculate and save, per layout driver >> Â - maximum layout size >> Â Â - take into account csr_fore_chan_attrs.ca_maxresponsesize and possible other parameters >> Â - keep a working copy of the maximum value and the calculated copy. >> Â - alignment value. >> - on miss, see if there's an adjacent layout segment in cache >> - if found, ask for twice the found segment size, up to the maximum value, >> Â aligned on the alignment value. >> - if the server returns less the layoutget range, keep note of the returned length >> Â (but not adjust maximum yet, as the server may return a short segment for various >> Â Âreasons) >> - if the server is consistent about returning less than was asked, adjust the >> Â - working copy of the maximum length >> - if the maximum was adjusted try bumping it up after X (TBD) layoutgets or T seconds >> Â to see if that was just due to high load or conflicts on the server >> - on any error returned for LAYOUTGET reset the algorithm parameters >> - on session reestablishment recalculate maximums. >> >> Benny >> > > I completely disagree with all this. NACK! > > The only proper thing a client can do is ask for what it needs, and only the application > can do that, because at the VFS level it is only second guessing, and is completely > pointless. > > The only one that can know about structure, alignments, optimal IO sizes and layouts > is the server. The server even have more information to second guess the application > from the file size information and it's share and lock disposition. Please see my > simple Server side algorithm. Well, IMO, client is closer to applications and should have a better position at "guessing" application's workload. A simple example, when a client asks for a layout, server would have no idea if client is doing layout prefetch, or if it really need that range to complete its work. But the client knows it for sure. > > Because you must understand one most important thing. Any smart decision a client can > make will be after it received the layout (stripe_unit, number-of-devices etc..) But > at that time it is too late it already sent the layout_get. Only the server knows > before hand what is the most optimal size. The client should just be a transparent > pipe from application to the server. It should never ever set policy. Only a Server > can/should do that. > > Lets put the efforts and algorithms where they belong, please? > > Boaz > -- Thanks, -Bergwolf -- 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
