Re: [PATCH v3 11/13] mm: zswap: Allocate acomp_batch_ctx resources for a given zswap_pool.

[Johannes Weiner]

On Wed, Nov 06, 2024 at 11:21:03AM -0800, Kanchana P Sridhar wrote:
> If the zswap_pool is associated with an acomp_alg/crypto_acomp that has
> registered batch_compress() and batch_decompress() API, we can allocate the
> necessary batching resources for the pool's acomp_batch_ctx.
> 
> This patch makes the above determination on incurring the per-cpu memory
> footprint cost for batching, and if so, goes ahead and allocates
> SWAP_CRYPTO_BATCH_SIZE (i.e. 8) acomp_reqs/buffers for the
> pool->acomp_batch_ctx on that specific cpu.
> 
> It also "remembers" the pool's batching readiness as a result of the above,
> through a new
> 
>    	enum batch_comp_status can_batch_comp;
> 
> member added to struct zswap_pool, for fast retrieval during
> zswap_store().
> 
> This allows us a way to only incur the memory footprint cost of the
> pool->acomp_batch_ctx resources for a given cpu on which zswap_store()
> needs to process a large folio.
> 
> Suggested-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
> Suggested-by: Ying Huang <ying.huang@xxxxxxxxx>
> Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx>

A general observation: this is a lot of code for a hardware specific
feature that many CPUs and architectures do not support. Please keep
the code self-contained, and wrap struct members and functions in a
new CONFIG option, so that not everybody has to compile this in.