Hi guys! On Thu 01-02-24 16:38:33, Ojaswin Mujoo wrote: > Thanks for the CC, I somehow missed this patch. > > As described in the discussion Jan linked [1] , there is a known bug in the > normalize code (which i should probably get back to now ) where we sometimes > end up with a goal range which doesn't completely cover the original extent and > this was causing issues when we tried to cover the complete original request in > the PA window adjustment logic. That and to minimize fragmentation, we ended up > going with the logic we have right now. > > In short, I agree that in the example Baokun pointed out, it is not > optimal to have to make an allocation request twice when we can get it in > one go. > > I also think Baokun is correct that if keeping the best extent at the end > doesn't cover the original start, then any other case should not lead to > it overflowing out of goal extent, including the case where original > extent is overflowing goal extent. Right, it was not obvious to me yesterday but when I've now reread how the normalization shifts the goal window, it is obvious. > So, as mentioned, it boils down to a trade off between multiple allocations and slightly > increased fragmentation. iiuc preallocations are anyways dropped when the file closes > so I think it shouldn't hurt too much fragmentation wise to prioritize less > allocations. What are your thoughts on this Jan, Baokun? OK, I'm fine with the Baokun's change if we remove the problematic BUG_ON. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
