+ mm-zswap-directly-use-percpu-mutex-and-buffer-in-load-store.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/zswap: directly use percpu mutex and buffer in load/store
has been added to the -mm mm-unstable branch.  Its filename is
     mm-zswap-directly-use-percpu-mutex-and-buffer-in-load-store.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-zswap-directly-use-percpu-mutex-and-buffer-in-load-store.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Chengming Zhou <zhouchengming@bytedance.com>
Subject: mm/zswap: directly use percpu mutex and buffer in load/store
Date: Mon, 18 Dec 2023 11:50:36 +0000

Since the introduce of reusing the dstmem in the load path, it seems
confusing that we are now using acomp_ctx->dstmem and acomp_ctx->mutex now
for purposes other than what the naming suggests.

Yosry suggested removing these two fields from acomp_ctx, and directly
using zswap_dstmem and zswap_mutex in both the load and store paths,
rename them, and add proper comments above their definitions that they are
for generic percpu buffering on the load and store paths.

So this patch remove dstmem and mutex from acomp_ctx, and rename the
zswap_dstmem to zswap_buffer, using the percpu mutex and buffer on the
load and store paths.

Link: https://lkml.kernel.org/r/20231213-zswap-dstmem-v3-6-4eac09b94ece@bytedance.com
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Suggested-by: Yosry Ahmed <yosryahmed@google.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/zswap.c |   69 +++++++++++++++++++++++++++------------------------
 1 file changed, 37 insertions(+), 32 deletions(-)

--- a/mm/zswap.c~mm-zswap-directly-use-percpu-mutex-and-buffer-in-load-store
+++ a/mm/zswap.c
@@ -166,8 +166,6 @@ struct crypto_acomp_ctx {
 	struct crypto_acomp *acomp;
 	struct acomp_req *req;
 	struct crypto_wait wait;
-	u8 *dstmem;
-	struct mutex *mutex;
 };
 
 /*
@@ -694,7 +692,7 @@ static void zswap_alloc_shrinker(struct
 /*********************************
 * per-cpu code
 **********************************/
-static DEFINE_PER_CPU(u8 *, zswap_dstmem);
+static DEFINE_PER_CPU(u8 *, zswap_buffer);
 /*
  * If users dynamically change the zpool type and compressor at runtime, i.e.
  * zswap is running, zswap can have more than one zpool on one cpu, but they
@@ -702,39 +700,39 @@ static DEFINE_PER_CPU(u8 *, zswap_dstmem
  */
 static DEFINE_PER_CPU(struct mutex *, zswap_mutex);
 
-static int zswap_dstmem_prepare(unsigned int cpu)
+static int zswap_buffer_prepare(unsigned int cpu)
 {
 	struct mutex *mutex;
-	u8 *dst;
+	u8 *buf;
 
-	dst = kmalloc_node(PAGE_SIZE, GFP_KERNEL, cpu_to_node(cpu));
-	if (!dst)
+	buf = kmalloc_node(PAGE_SIZE, GFP_KERNEL, cpu_to_node(cpu));
+	if (!buf)
 		return -ENOMEM;
 
 	mutex = kmalloc_node(sizeof(*mutex), GFP_KERNEL, cpu_to_node(cpu));
 	if (!mutex) {
-		kfree(dst);
+		kfree(buf);
 		return -ENOMEM;
 	}
 
 	mutex_init(mutex);
-	per_cpu(zswap_dstmem, cpu) = dst;
+	per_cpu(zswap_buffer, cpu) = buf;
 	per_cpu(zswap_mutex, cpu) = mutex;
 	return 0;
 }
 
-static int zswap_dstmem_dead(unsigned int cpu)
+static int zswap_buffer_dead(unsigned int cpu)
 {
 	struct mutex *mutex;
-	u8 *dst;
+	u8 *buf;
 
 	mutex = per_cpu(zswap_mutex, cpu);
 	kfree(mutex);
 	per_cpu(zswap_mutex, cpu) = NULL;
 
-	dst = per_cpu(zswap_dstmem, cpu);
-	kfree(dst);
-	per_cpu(zswap_dstmem, cpu) = NULL;
+	buf = per_cpu(zswap_buffer, cpu);
+	kfree(buf);
+	per_cpu(zswap_buffer, cpu) = NULL;
 
 	return 0;
 }
@@ -772,9 +770,6 @@ static int zswap_cpu_comp_prepare(unsign
 	acomp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
 				   crypto_req_done, &acomp_ctx->wait);
 
-	acomp_ctx->mutex = per_cpu(zswap_mutex, cpu);
-	acomp_ctx->dstmem = per_cpu(zswap_dstmem, cpu);
-
 	return 0;
 }
 
@@ -1397,15 +1392,21 @@ static void __zswap_load(struct zswap_en
 	struct zpool *zpool = zswap_find_zpool(entry);
 	struct scatterlist input, output;
 	struct crypto_acomp_ctx *acomp_ctx;
-	u8 *src;
+	u8 *src, *buf;
+	int cpu;
+	struct mutex *mutex;
 
-	acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
-	mutex_lock(acomp_ctx->mutex);
+	cpu = raw_smp_processor_id();
+	mutex = per_cpu(zswap_mutex, cpu);
+	mutex_lock(mutex);
+
+	acomp_ctx = per_cpu_ptr(entry->pool->acomp_ctx, cpu);
 
 	src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
 	if (!zpool_can_sleep_mapped(zpool)) {
-		memcpy(acomp_ctx->dstmem, src, entry->length);
-		src = acomp_ctx->dstmem;
+		buf = per_cpu(zswap_buffer, cpu);
+		memcpy(buf, src, entry->length);
+		src = buf;
 		zpool_unmap_handle(zpool, entry->handle);
 	}
 
@@ -1415,7 +1416,7 @@ static void __zswap_load(struct zswap_en
 	acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, PAGE_SIZE);
 	BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait));
 	BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
-	mutex_unlock(acomp_ctx->mutex);
+	mutex_unlock(mutex);
 
 	if (zpool_can_sleep_mapped(zpool))
 		zpool_unmap_handle(zpool, entry->handle);
@@ -1546,6 +1547,8 @@ bool zswap_store(struct folio *folio)
 	u8 *src, *dst;
 	gfp_t gfp;
 	int ret;
+	int cpu;
+	struct mutex *mutex;
 
 	VM_WARN_ON_ONCE(!folio_test_locked(folio));
 	VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
@@ -1631,11 +1634,13 @@ bool zswap_store(struct folio *folio)
 	}
 
 	/* compress */
-	acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
+	cpu = raw_smp_processor_id();
+	mutex = per_cpu(zswap_mutex, cpu);
+	mutex_lock(mutex);
 
-	mutex_lock(acomp_ctx->mutex);
+	acomp_ctx = per_cpu_ptr(entry->pool->acomp_ctx, cpu);
+	dst = per_cpu(zswap_buffer, cpu);
 
-	dst = acomp_ctx->dstmem;
 	sg_init_table(&input, 1);
 	sg_set_page(&input, page, PAGE_SIZE, 0);
 
@@ -1678,7 +1683,7 @@ bool zswap_store(struct folio *folio)
 	buf = zpool_map_handle(zpool, handle, ZPOOL_MM_WO);
 	memcpy(buf, dst, dlen);
 	zpool_unmap_handle(zpool, handle);
-	mutex_unlock(acomp_ctx->mutex);
+	mutex_unlock(mutex);
 
 	/* populate entry */
 	entry->swpentry = swp_entry(type, offset);
@@ -1721,7 +1726,7 @@ insert_entry:
 	return true;
 
 put_dstmem:
-	mutex_unlock(acomp_ctx->mutex);
+	mutex_unlock(mutex);
 put_pool:
 	zswap_pool_put(entry->pool);
 freepage:
@@ -1897,10 +1902,10 @@ static int zswap_setup(void)
 	}
 
 	ret = cpuhp_setup_state(CPUHP_MM_ZSWP_MEM_PREPARE, "mm/zswap:prepare",
-				zswap_dstmem_prepare, zswap_dstmem_dead);
+				zswap_buffer_prepare, zswap_buffer_dead);
 	if (ret) {
-		pr_err("dstmem alloc failed\n");
-		goto dstmem_fail;
+		pr_err("buffer alloc failed\n");
+		goto buffer_fail;
 	}
 
 	ret = cpuhp_setup_state_multi(CPUHP_MM_ZSWP_POOL_PREPARE,
@@ -1935,7 +1940,7 @@ fallback_fail:
 		zswap_pool_destroy(pool);
 hp_fail:
 	cpuhp_remove_state(CPUHP_MM_ZSWP_MEM_PREPARE);
-dstmem_fail:
+buffer_fail:
 	kmem_cache_destroy(zswap_entry_cache);
 cache_fail:
 	/* if built-in, we aren't unloaded on failure; don't allow use */
_

Patches currently in -mm which might be from zhouchengming@bytedance.com are

mm-zswap-change-dstmem-size-to-one-page.patch
mm-zswap-reuse-dstmem-when-decompress.patch
mm-zswap-refactor-out-__zswap_load.patch
mm-zswap-cleanup-zswap_load.patch
mm-zswap-cleanup-zswap_writeback_entry.patch
mm-zswap-directly-use-percpu-mutex-and-buffer-in-load-store.patch