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 Vu90iXxb 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wrote: > > > Back when per-vma locks were introduces, vm_lock was moved out of > > > vm_area_struct in [1] because of the performance regression caused by > > > false cacheline sharing. Recent investigation [2] revealed that the > > > regressions is limited to a rather old Broadwell microarchitecture and > > > even there it can be mitigated by disabling adjacent cacheline > > > prefetching, see [3]. > > > > I don't see a motivating reason as to why we want to do this? We increase > > memory usage here which is not good, but later lock optimisation mitigates > > it, but why wouldn't we just do the lock optimisations and use less memory > > overall? > > > > Where would you put the lock in that case though? > > With the patchset it sticks with the affected vma, so no false-sharing > woes concerning other instances of the same struct. > > If you make them separately allocated and packed, they false-share > between different vmas using them (in fact this is currently happening). > If you make sure to pad them, that's 64 bytes per obj, majority of which > is empty space. 'I don't see a motivating reason' = I don't see it in the commit message. I'm saying put motivating reasons, like the above, in the commit message.