[PATCH 3/7] mm/zswap: reuse dstmem when decompress

[Chengming Zhou <zhouchengming@bytedance.com>]

In the !zpool_can_sleep_mapped() case such as zsmalloc, we need to first
copy the entry->handle memory to a temporary memory, which is allocated
using kmalloc.

Obviously we can reuse the per-compressor dstmem to avoid allocating
every time, since it's percpu-compressor and protected in mutex.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
 mm/zswap.c | 29 +++++++++--------------------
 1 file changed, 9 insertions(+), 20 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index a6b4859a0164..d93a7b58b5af 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1758,9 +1758,9 @@ bool zswap_load(struct folio *folio)
 	struct zswap_entry *entry;
 	struct scatterlist input, output;
 	struct crypto_acomp_ctx *acomp_ctx;
-	u8 *src, *dst, *tmp;
+	unsigned int dlen = PAGE_SIZE;
+	u8 *src, *dst;
 	struct zpool *zpool;
-	unsigned int dlen;
 	bool ret;
 
 	VM_WARN_ON_ONCE(!folio_test_locked(folio));
@@ -1782,27 +1782,18 @@ bool zswap_load(struct folio *folio)
 		goto stats;
 	}
 
-	zpool = zswap_find_zpool(entry);
-	if (!zpool_can_sleep_mapped(zpool)) {
-		tmp = kmalloc(entry->length, GFP_KERNEL);
-		if (!tmp) {
-			ret = false;
-			goto freeentry;
-		}
-	}
-
 	/* decompress */
-	dlen = PAGE_SIZE;
-	src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
+	acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
+	mutex_lock(acomp_ctx->mutex);
 
+	zpool = zswap_find_zpool(entry);
+	src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
 	if (!zpool_can_sleep_mapped(zpool)) {
-		memcpy(tmp, src, entry->length);
-		src = tmp;
+		memcpy(acomp_ctx->dstmem, src, entry->length);
+		src = acomp_ctx->dstmem;
 		zpool_unmap_handle(zpool, entry->handle);
 	}
 
-	acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
-	mutex_lock(acomp_ctx->mutex);
 	sg_init_one(&input, src, entry->length);
 	sg_init_table(&output, 1);
 	sg_set_page(&output, page, PAGE_SIZE, 0);
@@ -1813,15 +1804,13 @@ bool zswap_load(struct folio *folio)
 
 	if (zpool_can_sleep_mapped(zpool))
 		zpool_unmap_handle(zpool, entry->handle);
-	else
-		kfree(tmp);
 
 	ret = true;
 stats:
 	count_vm_event(ZSWPIN);
 	if (entry->objcg)
 		count_objcg_event(entry->objcg, ZSWPIN);
-freeentry:
+
 	spin_lock(&tree->lock);
 	if (ret && zswap_exclusive_loads_enabled) {
 		zswap_invalidate_entry(tree, entry);

-- 
b4 0.10.1