[PATCH v9 08/26] netfs: Make mempool available for bvecq

[David Howells <dhowells@redhat.com>]

Make a mempool available for allocating bvecq structs.  Use it
automatically if anything other than GFP_KERNEL (with GFP_ZONEMASK flags
masked off) is specified.  Reading from a file can use GFP_KERNEL as the
failure mode is straightforward and the same for DIO reads and writes.
When it comes to writeback, however, the writeback_iter() API does not
permit temporary failure, including ENOMEM, if WB_SYNC_ALL is set and the
caller must process all folios to completion.  (I'm not sure if EINTR
constitutes an acceptable failure).

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Paulo Alcantara <pc@manguebit.org>
cc: Matthew Wilcox <willy@infradead.org>
cc: Christoph Hellwig <hch@infradead.org>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/bvecq.c      | 39 +++++++++++++++++++++++++++++++++------
 fs/netfs/internal.h   |  1 +
 fs/netfs/main.c       |  7 +++++++
 include/linux/bvecq.h |  3 +++
 4 files changed, 44 insertions(+), 6 deletions(-)

diff --git a/fs/netfs/bvecq.c b/fs/netfs/bvecq.c
index 00e321a796c9..0bd2ee70c656 100644
--- a/fs/netfs/bvecq.c
+++ b/fs/netfs/bvecq.c
@@ -46,8 +46,9 @@ EXPORT_SYMBOL(bvecq_dump);
  *
  * Allocate a single bvecq node and initialise the header.  A number of inline
  * slots are also allocated, rounded up to fit after the header in a power-of-2
- * slab object of up to 512 bytes (up to 29 slots on a 64-bit cpu).  The slot
- * array is not initialised.
+ * slab object of up to 512 bytes (up to 29 slots on a 64-bit cpu).  The caller
+ * should be aware that the number of slots allocated may be more or less than
+ * the number requested.  The slot array is not initialised.
  *
  * Return: The node pointer or NULL on allocation failure.
  */
@@ -58,16 +59,39 @@ struct bvecq *bvecq_alloc_one(size_t nr_slots, gfp_t gfp, bool for_writeback)
 	const size_t max_slots = (max_size - sizeof(*bq)) / sizeof(bq->__bv[0]);
 	size_t part = umin(nr_slots, max_slots);
 	size_t size = roundup_pow_of_two(struct_size(bq, __bv, part));
+	bool from_pool = false;
 
-	bq = kmalloc(size, gfp & ~GFP_ZONEMASK);
-	if (!bq)
-		return bq;
+	gfp &= ~GFP_ZONEMASK;
+
+	if (for_writeback) {
+		if (size != BVECQ_STD_SIZE) {
+			gfp_t gfp_temp = gfp;
 
+			gfp_temp |= __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN;
+			gfp_temp &= ~(__GFP_DIRECT_RECLAIM | __GFP_IO);
+			bq = kmalloc(size, gfp_temp);
+			if (bq)
+				goto success;
+		}
+
+		bq = mempool_alloc(&netfs_bvecq_pool, gfp);
+		if (!bq)
+			return bq;
+		from_pool = true;
+		size = BVECQ_STD_SIZE;
+	} else {
+		bq = kmalloc(size, gfp);
+		if (!bq)
+			return bq;
+	}
+
+success:
 	*bq = (struct bvecq) {
 		.ref		= REFCOUNT_INIT(1),
 		.bv		= bq->__bv,
 		.inline_bv	= true,
 		.max_slots	= (size - sizeof(*bq)) / sizeof(bq->__bv[0]),
+		.from_pool	= from_pool,
 	};
 	netfs_stat(&netfs_n_bvecq);
 	return bq;
@@ -247,7 +271,10 @@ void bvecq_put(struct bvecq *bq)
 			bvecq_free_slot(bq, slot);
 		next = bq->next;
 		netfs_stat_d(&netfs_n_bvecq);
-		kfree(bq);
+		if (bq->from_pool)
+			mempool_free(bq, &netfs_bvecq_pool);
+		else
+			kfree(bq);
 	}
 }
 EXPORT_SYMBOL(bvecq_put);
diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 46fb92601774..c68eea2ecc60 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -43,6 +43,7 @@ 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;
+extern mempool_t netfs_bvecq_pool;
 extern mempool_t netfs_folioq_pool;
 
 #ifdef CONFIG_PROC_FS
diff --git a/fs/netfs/main.c b/fs/netfs/main.c
index 927badf3989d..9f72e5054aff 100644
--- a/fs/netfs/main.c
+++ b/fs/netfs/main.c
@@ -28,6 +28,7 @@ static struct kmem_cache *netfs_request_slab;
 static struct kmem_cache *netfs_subrequest_slab;
 mempool_t netfs_request_pool;
 mempool_t netfs_subrequest_pool;
+mempool_t netfs_bvecq_pool;
 mempool_t netfs_folioq_pool;
 
 #ifdef CONFIG_PROC_FS
@@ -112,6 +113,9 @@ static int __init netfs_init(void)
 	if (mempool_init_kmalloc_pool(&netfs_folioq_pool, 100, sizeof(struct folio_queue)) < 0)
 		goto error_folioq_pool;
 
+	if (mempool_init_kmalloc_pool(&netfs_bvecq_pool, 100, BVECQ_STD_SIZE) < 0)
+		goto error_bvecq_pool;
+
 	netfs_request_slab = kmem_cache_create("netfs_request",
 					       sizeof(struct netfs_io_request), 0,
 					       SLAB_HWCACHE_ALIGN | SLAB_ACCOUNT,
@@ -164,6 +168,8 @@ static int __init netfs_init(void)
 error_reqpool:
 	kmem_cache_destroy(netfs_request_slab);
 error_req:
+	mempool_exit(&netfs_bvecq_pool);
+error_bvecq_pool:
 	mempool_exit(&netfs_folioq_pool);
 error_folioq_pool:
 	return ret;
@@ -178,6 +184,7 @@ static void __exit netfs_exit(void)
 	kmem_cache_destroy(netfs_subrequest_slab);
 	mempool_exit(&netfs_request_pool);
 	kmem_cache_destroy(netfs_request_slab);
+	mempool_exit(&netfs_bvecq_pool);
 	mempool_exit(&netfs_folioq_pool);
 }
 module_exit(netfs_exit);
diff --git a/include/linux/bvecq.h b/include/linux/bvecq.h
index 3d4ab0e554d4..07c96d1fa4b2 100644
--- a/include/linux/bvecq.h
+++ b/include/linux/bvecq.h
@@ -49,15 +49,18 @@ struct bvecq {
 	enum bvecq_mem	mem_type:3;	/* What sort of memory and how to free it */
 	bool		inline_bv:1;	/* T if __bv[] is being used */
 	bool		discontig:1;	/* T if not contiguous with previous bvecq */
+	bool		from_pool:1;	/* T if bvecq from mempool */
 	struct bio_vec	*bv;		/* Pointer to array of page fragments */
 	struct bio_vec	__bv[];		/* Default array (if ->inline_bv) */
 };
 
 #if BITS_PER_LONG == 64
 /* Number of slots in __bv[] for a bvecq in a 512-byte kmalloc block. */
+#define BVECQ_STD_SIZE		512
 #define BVECQ_STD_SLOTS		29	/* 2 words/slot; 32 slots; bvecq is 6 words (3 slots) */
 #elif  BITS_PER_LONG == 32
 /* Number of slots in __bv[] for a bvecq in a 256-byte kmalloc block. */
+#define BVECQ_STD_SIZE		256
 #define BVECQ_STD_SLOTS		18	/* 3 words/slot; 21 slots; bvecq is 9 words (3 slots) */
 #else
 #error BVECQ_STD_SLOTS undetermined