linux-kernel - [PATCH RFC 2/2] mm/zswap: remove the memcpy if acomp is not asynchronous

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Date: Wed,  3 Jan 2024 15:57:58 +1300
From: Barry Song <21cnbao@...il.com>
To: herbert@...dor.apana.org.au,
	davem@...emloft.net,
	akpm@...ux-foundation.org,
	chriscli@...gle.com,
	chrisl@...nel.org,
	ddstreet@...e.org,
	hannes@...xchg.org,
	linux-mm@...ck.org,
	nphamcs@...il.com,
	sjenning@...hat.com,
	vitaly.wool@...sulko.com,
	yosryahmed@...gle.com,
	zhouchengming@...edance.com
Cc: linux-kernel@...r.kernel.org,
	linux-crypto@...r.kernel.org,
	Barry Song <v-songbaohua@...o.com>
Subject: [PATCH RFC 2/2] mm/zswap: remove the memcpy if acomp is not asynchronous

From: Barry Song <v-songbaohua@...o.com>

Most compressors are actually CPU-based, they won't sleep during
decompression. we should be able to remove the redundant memcpy
for them.

Signed-off-by: Barry Song <v-songbaohua@...o.com>
---
 mm/zswap.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index ca25b676048e..36898614ebcc 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -168,6 +168,7 @@ struct crypto_acomp_ctx {
 	struct crypto_wait wait;
 	u8 *buffer;
 	struct mutex mutex;
+	bool is_async; /* if acomp can sleep */
 };
 
 /*
@@ -716,6 +717,7 @@ static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
 		goto acomp_fail;
 	}
 	acomp_ctx->acomp = acomp;
+	acomp_ctx->is_async = acomp_is_async(acomp);
 
 	req = acomp_request_alloc(acomp_ctx->acomp);
 	if (!req) {
@@ -1370,7 +1372,7 @@ static void __zswap_load(struct zswap_entry *entry, struct page *page)
 	mutex_lock(&acomp_ctx->mutex);
 
 	src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
-	if (!zpool_can_sleep_mapped(zpool)) {
+	if (acomp_ctx->is_async && !zpool_can_sleep_mapped(zpool)) {
 		memcpy(acomp_ctx->buffer, src, entry->length);
 		src = acomp_ctx->buffer;
 		zpool_unmap_handle(zpool, entry->handle);
@@ -1384,7 +1386,7 @@ static void __zswap_load(struct zswap_entry *entry, struct page *page)
 	BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
 	mutex_unlock(&acomp_ctx->mutex);
 
-	if (zpool_can_sleep_mapped(zpool))
+	if (!acomp_ctx->is_async || zpool_can_sleep_mapped(zpool))
 		zpool_unmap_handle(zpool, entry->handle);
 }
 
-- 
2.34.1