[PATCH v1 1/8] crypto: acomp - Define a unit_size in struct acomp_req to enable batching. mm: zswap: Set the unit size for zswap to PAGE_SIZE.

["Kanchana P. Sridhar" <kanchanapsridhar2026@gmail.com>]

We add a new @unit_size data member to struct acomp_req along with a
helper function acomp_request_set_unit_size() for kernel modules to set
the unit size to use while breaking down the request's src/dst
scatterlists.

An acomp_alg can implement batching by using the @req->unit_size to
break down the SG lists passed in via @req->dst and/or @req->src, to
submit individual @req->slen/@req->unit_size compress jobs or
@req->dlen/@req->unit_size decompress jobs, for batch compression and
batch decompression respectively.

In case of batch compression, the folio's pages for the batch can be
retrieved from the @req->src scatterlist by using a struct sg_page_iter
after determining the number of pages as @req->slen/@req->unit_size.

Please note that acomp_request_set_callback() sets the @req->unit_size
to 0.

In zswap_cpu_comp_prepare(), after the call to
acomp_request_set_callback(), we set the unit size for zswap to
PAGE_SIZE.

      acomp_request_set_unit_size(acomp_ctx->req, PAGE_SIZE);

Suggested-by: Herbert Xu <herbert@gondor.apana.org.au>
Co-developed-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
Signed-off-by: Kanchana P. Sridhar <kanchanapsridhar2026@gmail.com>
---
 include/crypto/acompress.h | 49 ++++++++++++++++++++++++++++++++++++++
 mm/zswap.c                 |  6 +++++
 2 files changed, 55 insertions(+)

diff --git a/include/crypto/acompress.h b/include/crypto/acompress.h
index 5d5358dfab73..6462fc46f4ec 100644
--- a/include/crypto/acompress.h
+++ b/include/crypto/acompress.h
@@ -79,6 +79,7 @@ struct acomp_req_chain {
  * @dvirt:	Destination virtual address
  * @slen:	Size of the input buffer
  * @dlen:	Size of the output buffer and number of bytes produced
+ * @unit_size:	Unit size for the request for use in batching
  * @chain:	Private API code data, do not use
  * @__ctx:	Start of private context data
  */
@@ -94,6 +95,7 @@ struct acomp_req {
 	};
 	unsigned int slen;
 	unsigned int dlen;
+	unsigned int unit_size;
 
 	struct acomp_req_chain chain;
 
@@ -329,9 +331,56 @@ static inline void acomp_request_set_callback(struct acomp_req *req,
 {
 	flgs &= ~CRYPTO_ACOMP_REQ_PRIVATE;
 	flgs |= req->base.flags & CRYPTO_ACOMP_REQ_PRIVATE;
+	req->unit_size = 0;
 	crypto_request_set_callback(&req->base, flgs, cmpl, data);
 }
 
+/**
+ * acomp_request_set_unit_size() -- Sets the unit size for the request.
+ *
+ * This is a helper function that enables batching for zswap, IPComp, etc.
+ * It allows multiple independent compression (or decompression) operations to
+ * be submitted in a single request's SG lists, where each SG list ("segment")
+ * is processed independently. The unit size helps derive segments from a
+ * single request. crypto_acomp does not expect the segments to be related in
+ * any way.
+ *
+ * Example usage model:
+ *
+ * A module such as zswap that's configured to use a batching compressor, can
+ * accomplish batch compression of "nr_pages" with crypto_acomp by creating an
+ * output SG table for the batch, initialized to contain "nr_pages" SG
+ * lists. Each scatterlist is mapped to the nth destination buffer for the
+ * batch. Depending on whether the @req is used for batch compress/decompress,
+ * zswap must set the @req's source/destination length to be
+ * "nr_pages * @req->unit_size" respectively.
+ *
+ * An acomp_alg can implement batch compression by using the @req->unit_size
+ * to break down the SG lists passed in via @req->dst to submit individual
+ * "@req->slen/@req->unit_size" compress jobs to be processed as a batch.
+ *
+ * Similarly, zswap can implement batch decompression by passing an
+ * SG table with "nr_pages" SG lists via @req->src to process
+ * "@req->dlen/@req->unit_size" decompress jobs as a batch.
+ *
+ * This API must be called after acomp_request_set_callback(),
+ * which sets @req->unit_size to 0. This makes it easy for users of
+ * crypto_acomp to rely on a default of not opting in to batching.
+ * Users such as zswap opt in to batching by defining @req->unit_size
+ * to a non-zero value for use by acomp_algs supporting batching.
+ *
+ * @du would be PAGE_SIZE for zswap, it could be the MTU for IPsec.
+ *
+ * @req:	asynchronous compress/decompress request
+ * @du:		data unit size of the input/output buffer scatterlist.
+ */
+static inline void acomp_request_set_unit_size(struct acomp_req *req,
+					       unsigned int du)
+{
+	req->unit_size = du;
+}
+
+
 /**
  * acomp_request_set_params() -- Sets request parameters
  *
diff --git a/mm/zswap.c b/mm/zswap.c
index ae19e301fced..ca513a9f89e3 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -845,6 +845,12 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
 	acomp_request_set_callback(acomp_ctx->req, CRYPTO_TFM_REQ_MAY_BACKLOG,
 				   crypto_req_done, &acomp_ctx->wait);
 
+	/*
+	 * This should be called after acomp_request_set_callback(),
+	 * which initializes req->unit_size to 0.
+	 */
+	acomp_request_set_unit_size(acomp_ctx->req, PAGE_SIZE);
+
 	mutex_init(&acomp_ctx->mutex);
 	return 0;
 
-- 
2.39.5