netfs: Use mempools for allocating requests and subrequests

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

@@ -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)

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);

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);
 }

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);