[..] > > > > > > > > There are no other callers to these functions. Just do the work > > > > directly in the cpu callbacks here like it used to be. > > > > > > There will be other callers to zswap_create_acomp_ctx() and > > > zswap_delete_acomp_ctx() in patches 10 and 11 of this series, when the > > > per-cpu "acomp_batch_ctx" is introduced in struct zswap_pool. I was trying > > > to modularize the code first, so as to split the changes into smaller commits. > > > > > > The per-cpu "acomp_batch_ctx" resources are allocated in patch 11 in the > > > "zswap_pool_can_batch()" function, that allocates batching resources > > > for this cpu. This was to address Yosry's earlier comment about minimizing > > > the memory footprint cost of batching. > > > > > > The way I decided to do this is by reusing the code that allocates the de- > > facto > > > pool->acomp_ctx for the selected compressor for all cpu's in > > zswap_pool_create(). > > > However, I did not want to add the acomp_batch_ctx multiple reqs/buffers > > > allocation to the cpuhp_state_add_instance() code path which would incur > > the > > > memory cost on all cpu's. > > > > > > Instead, the approach I chose to follow is to allocate the batching resources > > > in patch 11 only as needed, on "a given cpu" that has to store a large folio. > > Hope > > > this explains the purpose of the modularization better. > > > > > > Other ideas towards accomplishing this are very welcome. > > > > If we remove the sysctl as suggested by Johannes, then we can just > > allocate the number of buffers based on the compressor and whether it > > supports batching during the pool initialization in the cpu callbacks > > only. > > > > Right? > > Yes, we could do that if the sysctl is removed, as suggested by Johannes. > The only "drawback" of allocating the batching resources (assuming the > compressor allows batching) would be that the memory footprint penalty > would be incurred on every cpu. I was trying to further economize this > cost based on whether a given cpu actually needs to zswap_store() a > large folio, and only then allocate the batching resources. Although, I am > not sure if this would benefit any usage model. > > If we agree the pool initialization is the best place to allocate the batching > resources, then I will make this change in v4. IIUC the additional cost would apply if someone wants to use deflate-iaa on hardware that supports batching but does not want to use batching. I don't think catering to such a use case warrants the complexity in advance, not until we have a user that genuinely cares.
