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>>> + /* >>> + * Back to atomic context. First, check if we migrated to a new >>> + * CPU with a usable percpu cluster. If so, try using that instead. >>> + * No need to check it for the spinning device, as swap is >>> + * serialized by the global lock on them. >>> + * >>> + * The is_usable check is a bit rough, but ensures order 0 success. >>> + */ >>> + offset = this_cpu_read(percpu_swap_cluster.offset[order]); >>> + if ((si->flags & SWP_SOLIDSTATE) && offset) { >>> + pcp_ci = swap_cluster_lock(si, offset); >>> + if (cluster_is_usable(pcp_ci, order) && >>> + pcp_ci->count < SWAPFILE_CLUSTER) { >>> + ci = pcp_ci; >> ^^^^^^^^^^^^^ >> ci came from the caller, and in the case of isolate_lock_cluster() they >> had just removed it from a list. We overwrite ci and return something >> different. > > Yes, that's expected. See the comment above. We have just dropped > local lock so it's possible that we migrated to another CPU which has > its own percpu cache ci (percpu_swap_cluster.offset). > > To avoid fragmentation, drop the isolated ci and use the percpu ci > instead. But you are right that I need to add the ci back to the list, > or it will be leaked. Thanks! Yeah, the comment helped a lot (thank you). It was just the leak I was worried about ;) -chris