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 > - maximum layout size > - take into account csr_fore_chan_attrs.ca_maxresponsesize and possible other parameters > - keep a working copy of the maximum value and the calculated copy. > - 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, > aligned on the alignment value. > - if the server returns less the layoutget range, keep note of the returned length > (but not adjust maximum yet, as the server may return a short segment for various > reasons) > - if the server is consistent about returning less than was asked, adjust the > - working copy of the maximum length > - if the maximum was adjusted try bumping it up after X (TBD) layoutgets or T seconds > 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. 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 -- 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
