[PATCH v2 11/22] netfs: Use mempools for allocating requests and subrequests

[David Howells <dhowells@redhat.com>]

Use mempools for allocating requests and subrequests in an effort to make
sure that allocation always succeeds so that when performing writeback we
can always make progress.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
---
 fs/netfs/internal.h   |  2 ++
 fs/netfs/main.c       | 51 ++++++++++++++++++++++++++++++++-----
 fs/netfs/objects.c    | 59 ++++++++++++++++++++++++++++---------------
 include/linux/netfs.h |  5 ++--
 4 files changed, 89 insertions(+), 28 deletions(-)

diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 156ab138e224..c67da478cd2b 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -37,6 +37,8 @@ int netfs_begin_read(struct netfs_io_request *rreq, bool sync);
 extern unsigned int netfs_debug;
 extern struct list_head netfs_io_requests;
 extern spinlock_t netfs_proc_lock;
+extern mempool_t netfs_request_pool;
+extern mempool_t netfs_subrequest_pool;
 
 #ifdef CONFIG_PROC_FS
 static inline void netfs_proc_add_rreq(struct netfs_io_request *rreq)
diff --git a/fs/netfs/main.c b/fs/netfs/main.c
index 844efbb2e7a2..4805b9377364 100644
--- a/fs/netfs/main.c
+++ b/fs/netfs/main.c
@@ -7,6 +7,7 @@
 
 #include <linux/module.h>
 #include <linux/export.h>
+#include <linux/mempool.h>
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 #include "internal.h"
@@ -23,6 +24,11 @@ unsigned netfs_debug;
 module_param_named(debug, netfs_debug, uint, S_IWUSR | S_IRUGO);
 MODULE_PARM_DESC(netfs_debug, "Netfs support debugging mask");
 
+static struct kmem_cache *netfs_request_slab;
+static struct kmem_cache *netfs_subrequest_slab;
+mempool_t netfs_request_pool;
+mempool_t netfs_subrequest_pool;
+
 #ifdef CONFIG_PROC_FS
 LIST_HEAD(netfs_io_requests);
 DEFINE_SPINLOCK(netfs_proc_lock);
@@ -98,25 +104,54 @@ static int __init netfs_init(void)
 {
 	int ret = -ENOMEM;
 
+	netfs_request_slab = kmem_cache_create("netfs_request",
+					       sizeof(struct netfs_io_request), 0,
+					       SLAB_HWCACHE_ALIGN | SLAB_ACCOUNT,
+					       NULL);
+	if (!netfs_request_slab)
+		goto error_req;
+
+	if (mempool_init_slab_pool(&netfs_request_pool, 100, netfs_request_slab) < 0)
+		goto error_reqpool;
+
+	netfs_subrequest_slab = kmem_cache_create("netfs_subrequest",
+						  sizeof(struct netfs_io_subrequest), 0,
+						  SLAB_HWCACHE_ALIGN | SLAB_ACCOUNT,
+						  NULL);
+	if (!netfs_subrequest_slab)
+		goto error_subreq;
+
+	if (mempool_init_slab_pool(&netfs_subrequest_pool, 100, netfs_subrequest_slab) < 0)
+		goto error_subreqpool;
+
 	if (!proc_mkdir("fs/netfs", NULL))
-		goto error;
+		goto error_proc;
 	if (!proc_create_seq("fs/netfs/requests", S_IFREG | 0444, NULL,
 			     &netfs_requests_seq_ops))
-		goto error_proc;
+		goto error_procfile;
 #ifdef CONFIG_FSCACHE_STATS
 	if (!proc_create_single("fs/netfs/stats", S_IFREG | 0444, NULL,
 				netfs_stats_show))
-		goto error_proc;
+		goto error_procfile;
 #endif
 
 	ret = fscache_init();
 	if (ret < 0)
-		goto error_proc;
+		goto error_fscache;
 	return 0;
 
-error_proc:
+error_fscache:
+error_procfile:
 	remove_proc_entry("fs/netfs", NULL);
-error:
+error_proc:
+	mempool_exit(&netfs_subrequest_pool);
+error_subreqpool:
+	kmem_cache_destroy(netfs_subrequest_slab);
+error_subreq:
+	mempool_exit(&netfs_request_pool);
+error_reqpool:
+	kmem_cache_destroy(netfs_request_slab);
+error_req:
 	return ret;
 }
 fs_initcall(netfs_init);
@@ -125,5 +160,9 @@ static void __exit netfs_exit(void)
 {
 	fscache_exit();
 	remove_proc_entry("fs/netfs", NULL);
+	mempool_exit(&netfs_subrequest_pool);
+	kmem_cache_destroy(netfs_subrequest_slab);
+	mempool_exit(&netfs_request_pool);
+	kmem_cache_destroy(netfs_request_slab);
 }
 module_exit(netfs_exit);
diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
index 8acc03a64059..1a4e2ce735ce 100644
--- a/fs/netfs/objects.c
+++ b/fs/netfs/objects.c
@@ -6,6 +6,8 @@
  */
 
 #include <linux/slab.h>
+#include <linux/mempool.h>
+#include <linux/delay.h>
 #include "internal.h"
 
 /*
@@ -20,17 +22,22 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 	struct inode *inode = file ? file_inode(file) : mapping->host;
 	struct netfs_inode *ctx = netfs_inode(inode);
 	struct netfs_io_request *rreq;
+	mempool_t *mempool = ctx->ops->request_pool ?: &netfs_request_pool;
+	struct kmem_cache *cache = mempool->pool_data;
 	bool is_unbuffered = (origin == NETFS_UNBUFFERED_WRITE ||
 			      origin == NETFS_DIO_READ ||
 			      origin == NETFS_DIO_WRITE);
 	bool cached = !is_unbuffered && netfs_is_cache_enabled(ctx);
 	int ret;
 
-	rreq = kzalloc(ctx->ops->io_request_size ?: sizeof(struct netfs_io_request),
-		       GFP_KERNEL);
-	if (!rreq)
-		return ERR_PTR(-ENOMEM);
+	for (;;) {
+		rreq = mempool_alloc(mempool, GFP_KERNEL);
+		if (rreq)
+			break;
+		msleep(10);
+	}
 
+	memset(rreq, 0, kmem_cache_size(cache));
 	rreq->start	= start;
 	rreq->len	= len;
 	rreq->upper_len	= len;
@@ -56,7 +63,7 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 	if (rreq->netfs_ops->init_request) {
 		ret = rreq->netfs_ops->init_request(rreq, file);
 		if (ret < 0) {
-			kfree(rreq);
+			mempool_free(rreq, rreq->netfs_ops->request_pool ?: &netfs_request_pool);
 			return ERR_PTR(ret);
 		}
 	}
@@ -88,6 +95,14 @@ void netfs_clear_subrequests(struct netfs_io_request *rreq, bool was_async)
 	}
 }
 
+static void netfs_free_request_rcu(struct rcu_head *rcu)
+{
+	struct netfs_io_request *rreq = container_of(rcu, struct netfs_io_request, rcu);
+
+	mempool_free(rreq, rreq->netfs_ops->request_pool ?: &netfs_request_pool);
+	netfs_stat_d(&netfs_n_rh_rreq);
+}
+
 static void netfs_free_request(struct work_struct *work)
 {
 	struct netfs_io_request *rreq =
@@ -110,8 +125,7 @@ static void netfs_free_request(struct work_struct *work)
 		}
 		kvfree(rreq->direct_bv);
 	}
-	kfree_rcu(rreq, rcu);
-	netfs_stat_d(&netfs_n_rh_rreq);
+	call_rcu(&rreq->rcu, netfs_free_request_rcu);
 }
 
 void netfs_put_request(struct netfs_io_request *rreq, bool was_async,
@@ -143,20 +157,25 @@ void netfs_put_request(struct netfs_io_request *rreq, bool was_async,
 struct netfs_io_subrequest *netfs_alloc_subrequest(struct netfs_io_request *rreq)
 {
 	struct netfs_io_subrequest *subreq;
-
-	subreq = kzalloc(rreq->netfs_ops->io_subrequest_size ?:
-			 sizeof(struct netfs_io_subrequest),
-			 GFP_KERNEL);
-	if (subreq) {
-		INIT_WORK(&subreq->work, NULL);
-		INIT_LIST_HEAD(&subreq->rreq_link);
-		refcount_set(&subreq->ref, 2);
-		subreq->rreq = rreq;
-		subreq->debug_index = atomic_inc_return(&rreq->subreq_counter);
-		netfs_get_request(rreq, netfs_rreq_trace_get_subreq);
-		netfs_stat(&netfs_n_rh_sreq);
+	mempool_t *mempool = rreq->netfs_ops->subrequest_pool ?: &netfs_subrequest_pool;
+	struct kmem_cache *cache = mempool->pool_data;
+
+	for (;;) {
+		subreq = mempool_alloc(rreq->netfs_ops->subrequest_pool ?: &netfs_subrequest_pool,
+				       GFP_KERNEL);
+		if (subreq)
+			break;
+		msleep(10);
 	}
 
+	memset(subreq, 0, kmem_cache_size(cache));
+	INIT_WORK(&subreq->work, NULL);
+	INIT_LIST_HEAD(&subreq->rreq_link);
+	refcount_set(&subreq->ref, 2);
+	subreq->rreq = rreq;
+	subreq->debug_index = atomic_inc_return(&rreq->subreq_counter);
+	netfs_get_request(rreq, netfs_rreq_trace_get_subreq);
+	netfs_stat(&netfs_n_rh_sreq);
 	return subreq;
 }
 
@@ -178,7 +197,7 @@ static void netfs_free_subrequest(struct netfs_io_subrequest *subreq,
 	trace_netfs_sreq(subreq, netfs_sreq_trace_free);
 	if (rreq->netfs_ops->free_subrequest)
 		rreq->netfs_ops->free_subrequest(subreq);
-	kfree(subreq);
+	mempool_free(subreq, rreq->netfs_ops->subrequest_pool ?: &netfs_subrequest_pool);
 	netfs_stat_d(&netfs_n_rh_sreq);
 	netfs_put_request(rreq, was_async, netfs_rreq_trace_put_subreq);
 }
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 3af589dabd7f..0b6c2c2d3c23 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -20,6 +20,7 @@
 #include <linux/uio.h>
 
 enum netfs_sreq_ref_trace;
+typedef struct mempool_s mempool_t;
 
 /**
  * folio_start_private_2 - Start an fscache write on a folio.  [DEPRECATED]
@@ -236,8 +237,8 @@ struct netfs_io_request {
  * Operations the network filesystem can/must provide to the helpers.
  */
 struct netfs_request_ops {
-	unsigned int	io_request_size;	/* Alloc size for netfs_io_request struct */
-	unsigned int	io_subrequest_size;	/* Alloc size for netfs_io_subrequest struct */
+	mempool_t *request_pool;
+	mempool_t *subrequest_pool;
 	int (*init_request)(struct netfs_io_request *rreq, struct file *file);
 	void (*free_request)(struct netfs_io_request *rreq);
 	void (*free_subrequest)(struct netfs_io_subrequest *rreq);