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? :) > > -- > Best Regards, > Huang, Ying >
