Ryan Roberts <ryan.roberts@xxxxxxx> writes: > On 12/03/2024 07:52, Huang, Ying wrote: >> Ryan Roberts <ryan.roberts@xxxxxxx> writes: >> >>> struct percpu_cluster stores the index of cpu's current cluster and the >>> offset of the next entry that will be allocated for the cpu. These two >>> pieces of information are redundant because the cluster index is just >>> (offset / SWAPFILE_CLUSTER). The only reason for explicitly keeping the >>> cluster index is because the structure used for it also has a flag to >>> indicate "no cluster". However this data structure also contains a spin >>> lock, which is never used in this context, as a side effect the code >>> copies the spinlock_t structure, which is questionable coding practice >>> in my view. >>> >>> So let's clean this up and store only the next offset, and use a >>> sentinal value (SWAP_NEXT_INVALID) to indicate "no cluster". >>> SWAP_NEXT_INVALID is chosen to be 0, because 0 will never be seen >>> legitimately; The first page in the swap file is the swap header, which >>> is always marked bad to prevent it from being allocated as an entry. >>> This also prevents the cluster to which it belongs being marked free, so >>> it will never appear on the free list. >>> >>> This change saves 16 bytes per cpu. And given we are shortly going to >>> extend this mechanism to be per-cpu-AND-per-order, we will end up saving >>> 16 * 9 = 144 bytes per cpu, which adds up if you have 256 cpus in the >>> system. >>> >>> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> >> >> LGTM, Thanks! > > Thanks! What's a guy got to do to get Rb or Ack? :) Feel free to add Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx> in the future version. -- Best Regards, Huang, Ying
