linux-kernel - Re: [PATCH v3 11/13] mm: zswap: Allocate acomp_batch_ctx resources for a given zswap

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Message-ID: <20241107173124.GD1172372@cmpxchg.org>
Date: Thu, 7 Nov 2024 12:31:24 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Kanchana P Sridhar <kanchana.p.sridhar@...el.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, yosryahmed@...gle.com,
	nphamcs@...il.com, chengming.zhou@...ux.dev, usamaarif642@...il.com,
	ryan.roberts@....com, ying.huang@...el.com, 21cnbao@...il.com,
	akpm@...ux-foundation.org, linux-crypto@...r.kernel.org,
	herbert@...dor.apana.org.au, davem@...emloft.net,
	clabbe@...libre.com, ardb@...nel.org, ebiggers@...gle.com,
	surenb@...gle.com, kristen.c.accardi@...el.com, zanussi@...nel.org,
	wajdi.k.feghali@...el.com, vinodh.gopal@...el.com
Subject: Re: [PATCH v3 11/13] mm: zswap: Allocate acomp_batch_ctx resources
 for a given zswap_pool.

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@...gle.com>
> Suggested-by: Ying Huang <ying.huang@...el.com>
> Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@...el.com>

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.