[RFC 3/3] scsi: target: tcmu: Support zero copy

[Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>]

Currently in tcmu, for READ commands, it copies user space backstore's
data buffer to tcmu internal data area, then copies data in data area
to READ commands sgl pages. For WRITE commands, tcmu copies sgl pages
to tcmu internal data area, then copies data in data area to user space
backstore. For both cases, there are obvious copy overhead, which impact
io throughput, especially for large io size.

To mitigate this issue, we implement zero copy feature to tcmu, which
map sgl pages to user space backstore's address space. Currently only
sgl pages's offset and length are both aligned to page size, can this
command go into tcmu zero copy path.

Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
---
 drivers/target/target_core_user.c | 257 +++++++++++++++++++++++++++++++++-----
 1 file changed, 229 insertions(+), 28 deletions(-)

diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index 7b2a89a67cdb..4314e0c00f8e 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -16,6 +16,8 @@
 #include <linux/xarray.h>
 #include <linux/stringify.h>
 #include <linux/bitops.h>
+#include <linux/sched/mm.h>
+#include <linux/mm.h>
 #include <linux/highmem.h>
 #include <linux/configfs.h>
 #include <linux/mutex.h>
@@ -72,6 +74,7 @@
  */
 #define DATA_PAGES_PER_BLK_DEF 1
 #define DATA_AREA_PAGES_DEF (256 * 1024)
+#define ZC_DATA_AREA_PAGES_DEF (256 * 1024)
 
 #define TCMU_MBS_TO_PAGES(_mbs) ((size_t)_mbs << (20 - PAGE_SHIFT))
 #define TCMU_PAGES_TO_MBS(_pages) (_pages >> (20 - PAGE_SHIFT))
@@ -145,9 +148,20 @@ struct tcmu_dev {
 	struct list_head qfull_queue;
 	struct list_head tmr_queue;
 
+	/* For zero copy handle */
+	int zc_data_area_mb;
+	uint32_t zc_max_blocks;
 	uint32_t dbi_max;
 	uint32_t dbi_thresh;
 	unsigned long *data_bitmap;
+
+	struct mm_struct *vma_vm_mm;
+	struct vm_area_struct *vma;
+
+	uint32_t zc_dbi_max;
+	uint32_t zc_dbi_thresh;
+	unsigned long *zc_data_bitmap;
+
 	struct xarray data_pages;
 	uint32_t data_pages_per_blk;
 	uint32_t data_blk_size;
@@ -177,6 +191,12 @@ struct tcmu_cmd {
 	struct tcmu_dev *tcmu_dev;
 	struct list_head queue_entry;
 
+	/* For zero_copy handle */
+	struct mm_struct *vma_vm_mm;
+	struct vm_area_struct *vma;
+	struct iovec *iov;
+	int iov_cnt;
+
 	uint16_t cmd_id;
 
 	/* Can't use se_cmd when cleaning up expired cmds, because if
@@ -192,6 +212,7 @@ struct tcmu_cmd {
 
 #define TCMU_CMD_BIT_EXPIRED 0
 #define TCMU_CMD_BIT_KEEP_BUF 1
+#define TCMU_CMD_BIT_ZEROCOPY 2
 	unsigned long flags;
 };
 
@@ -495,10 +516,16 @@ static struct genl_family tcmu_genl_family __ro_after_init = {
 static void tcmu_cmd_free_data(struct tcmu_cmd *tcmu_cmd, uint32_t len)
 {
 	struct tcmu_dev *udev = tcmu_cmd->tcmu_dev;
+	unsigned long *data_bitmap;
 	uint32_t i;
 
+	if (test_bit(TCMU_CMD_BIT_ZEROCOPY, &tcmu_cmd->flags))
+		data_bitmap = udev->zc_data_bitmap;
+	else
+		data_bitmap = udev->data_bitmap;
+
 	for (i = 0; i < len; i++)
-		clear_bit(tcmu_cmd->dbi[i], udev->data_bitmap);
+		clear_bit(tcmu_cmd->dbi[i], data_bitmap);
 }
 
 static inline int tcmu_get_empty_block(struct tcmu_dev *udev,
@@ -549,8 +576,30 @@ static inline int tcmu_get_empty_block(struct tcmu_dev *udev,
 	return i == page_cnt ? dbi : -1;
 }
 
+static inline int tcmu_get_zc_empty_block(struct tcmu_dev *udev,
+			struct tcmu_cmd *tcmu_cmd, int prev_dbi,
+			int *iov_cnt)
+{
+	int dbi;
+
+	dbi = find_first_zero_bit(udev->zc_data_bitmap, udev->zc_dbi_thresh);
+	if (dbi == udev->zc_dbi_thresh)
+		return -1;
+
+	if (dbi > udev->zc_dbi_max)
+		udev->zc_dbi_max = dbi;
+
+	set_bit(dbi, udev->zc_data_bitmap);
+	tcmu_cmd_set_dbi(tcmu_cmd, dbi);
+
+	if (dbi != prev_dbi + 1)
+		*iov_cnt += 1;
+	return dbi;
+}
+
 static int tcmu_get_empty_blocks(struct tcmu_dev *udev,
-				 struct tcmu_cmd *tcmu_cmd, int length)
+				 struct tcmu_cmd *tcmu_cmd, int length,
+				 bool zero_copy)
 {
 	/* start value of dbi + 1 must not be a valid dbi */
 	int dbi = -2;
@@ -559,16 +608,111 @@ static int tcmu_get_empty_blocks(struct tcmu_dev *udev,
 
 	for (; length > 0; length -= blk_size) {
 		blk_data_len = min_t(uint32_t, length, blk_size);
-		dbi = tcmu_get_empty_block(udev, tcmu_cmd, dbi, blk_data_len,
-					   &iov_cnt);
+		if (zero_copy) {
+			dbi = tcmu_get_zc_empty_block(udev, tcmu_cmd, dbi,
+						      &iov_cnt);
+		} else {
+			dbi = tcmu_get_empty_block(udev, tcmu_cmd, dbi,
+					blk_data_len, &iov_cnt);
+		}
 		if (dbi < 0)
 			return -1;
 	}
 	return iov_cnt;
 }
 
+#define TCMU_ZEROCOPY_PAGE_BATCH 32
+
+static inline void tcmu_zerocopy_one_seg(struct iovec *iov,
+			struct vm_area_struct *vma,
+			struct sg_page_iter *sgiter)
+{
+	struct page *pages[TCMU_ZEROCOPY_PAGE_BATCH];
+	unsigned int len = iov->iov_len;
+	unsigned long address = (unsigned long)iov->iov_base + vma->vm_start;
+	unsigned long pages_remaining, pg_index = 0;
+	struct page *page;
+
+	while (len > 0) {
+		__sg_page_iter_next(sgiter);
+		page = sg_page_iter_page(sgiter);
+		pages[pg_index++] = page;
+		len -= PAGE_SIZE;
+		if (pg_index == TCMU_ZEROCOPY_PAGE_BATCH || !len) {
+			pages_remaining = pg_index;
+			vm_insert_pages_mkspecial(vma, address, pages, &pages_remaining);
+			address = address + pg_index * PAGE_SIZE;
+			pg_index = 0;
+		}
+	}
+}
+
+static long tcmu_cmd_zerocopy_map(struct tcmu_dev *udev,
+				  struct tcmu_cmd *cmd,
+				  struct iovec *iov,
+				  int iov_cnt)
+{
+	struct se_cmd *se_cmd = cmd->se_cmd;
+	struct scatterlist *data_sg;
+	unsigned int data_nents;
+	struct iovec *tiov;
+	struct sg_page_iter sgiter;
+	struct vm_area_struct *vma = udev->vma;
+	int i, ret = 0;
+
+	mmap_read_lock(udev->vma_vm_mm);
+	data_sg = se_cmd->t_data_sg;
+	data_nents = se_cmd->t_data_nents;
+	__sg_page_iter_start(&sgiter, data_sg, data_nents, 0);
+	tiov = iov;
+	for (i = 0; i < iov_cnt; i++) {
+		tcmu_zerocopy_one_seg(tiov, vma, &sgiter);
+		tiov++;
+	}
+	cmd->iov = iov;
+	cmd->iov_cnt = iov_cnt;
+	cmd->vma_vm_mm = vma->vm_mm;
+	cmd->vma = vma;
+	mmgrab(cmd->vma_vm_mm);
+	mmap_read_unlock(udev->vma_vm_mm);
+	return ret;
+}
+
+static void tcmu_cmd_zerocopy_unmap(struct tcmu_cmd *cmd)
+{
+	struct mm_struct *mm;
+	struct vm_area_struct *vma;
+	struct iovec *iov;
+	unsigned long address;
+	int i;
+
+	mm = cmd->vma_vm_mm;
+	if (!mm)
+		return;
+
+	vma = cmd->vma;
+	iov = cmd->iov;
+	if (mmget_not_zero(mm)) {
+		mmap_read_lock(mm);
+		for (i = 0; i < cmd->iov_cnt; i++) {
+			address = (unsigned long)iov->iov_base + vma->vm_start;
+			zap_page_range(vma, address, iov->iov_len);
+			iov++;
+		}
+		mmap_read_unlock(mm);
+		mmput(mm);
+	}
+
+	cmd->vma_vm_mm = NULL;
+	cmd->vma = NULL;
+	mmdrop(mm);
+}
+
 static inline void tcmu_free_cmd(struct tcmu_cmd *tcmu_cmd)
 {
+	if (test_bit(TCMU_CMD_BIT_ZEROCOPY, &tcmu_cmd->flags))
+		tcmu_cmd_zerocopy_unmap(tcmu_cmd);
+
 	kfree(tcmu_cmd->dbi);
 	kmem_cache_free(tcmu_cmd_cache, tcmu_cmd);
 }
@@ -850,37 +994,57 @@ static bool is_ring_space_avail(struct tcmu_dev *udev, size_t cmd_size)
  * Called with ring lock held.
  */
 static int tcmu_alloc_data_space(struct tcmu_dev *udev, struct tcmu_cmd *cmd,
-				  int *iov_bidi_cnt)
+				  int *iov_bidi_cnt, bool zero_copy)
 {
 	int space, iov_cnt = 0, ret = 0;
 
 	if (!cmd->dbi_cnt)
 		goto wr_iov_cnts;
 
-	/* try to check and get the data blocks as needed */
-	space = spc_bitmap_free(udev->data_bitmap, udev->dbi_thresh);
-	if (space < cmd->dbi_cnt) {
-		unsigned long blocks_left =
-				(udev->max_blocks - udev->dbi_thresh) + space;
+	if (!zero_copy) {
+		/* try to check and get the data blocks as needed */
+		space = spc_bitmap_free(udev->data_bitmap, udev->dbi_thresh);
+		if (space < cmd->dbi_cnt) {
+			unsigned long blocks_left =
+					(udev->max_blocks - udev->dbi_thresh) + space;
+
+			if (blocks_left < cmd->dbi_cnt) {
+				pr_debug("no data space: only %lu available, but ask for %u\n",
+						blocks_left * udev->data_blk_size,
+						cmd->dbi_cnt * udev->data_blk_size);
+				return -1;
+			}
 
-		if (blocks_left < cmd->dbi_cnt) {
-			pr_debug("no data space: only %lu available, but ask for %u\n",
-					blocks_left * udev->data_blk_size,
-					cmd->dbi_cnt * udev->data_blk_size);
-			return -1;
+			udev->dbi_thresh += cmd->dbi_cnt;
+			if (udev->dbi_thresh > udev->max_blocks)
+				udev->dbi_thresh = udev->max_blocks;
 		}
+	} else {
+		/* try to check and get the data blocks as needed */
+		space = spc_bitmap_free(udev->zc_data_bitmap, udev->zc_dbi_thresh);
+		if (space < cmd->dbi_cnt) {
+			unsigned long blocks_left =
+					(udev->zc_max_blocks - udev->zc_dbi_thresh) + space;
+
+			if (blocks_left < cmd->dbi_cnt) {
+				pr_debug("no data space: only %lu available, but ask for %u\n",
+						blocks_left * udev->data_blk_size,
+						cmd->dbi_cnt * udev->data_blk_size);
+				return -1;
+			}
 
-		udev->dbi_thresh += cmd->dbi_cnt;
-		if (udev->dbi_thresh > udev->max_blocks)
-			udev->dbi_thresh = udev->max_blocks;
+			udev->zc_dbi_thresh += cmd->dbi_cnt;
+			if (udev->zc_dbi_thresh > udev->zc_max_blocks)
+				udev->zc_dbi_thresh = udev->zc_max_blocks;
+		}
 	}
 
-	iov_cnt = tcmu_get_empty_blocks(udev, cmd, cmd->se_cmd->data_length);
+	iov_cnt = tcmu_get_empty_blocks(udev, cmd, cmd->se_cmd->data_length, zero_copy);
 	if (iov_cnt < 0)
 		return -1;
 
 	if (cmd->dbi_bidi_cnt) {
-		ret = tcmu_get_empty_blocks(udev, cmd, cmd->data_len_bidi);
+		ret = tcmu_get_empty_blocks(udev, cmd, cmd->data_len_bidi, zero_copy);
 		if (ret < 0)
 			return -1;
 	}
@@ -1021,6 +1185,7 @@ static int queue_cmd_ring(struct tcmu_cmd *tcmu_cmd, sense_reason_t *scsi_err)
 	uint32_t blk_size = udev->data_blk_size;
 	/* size of data buffer needed */
 	size_t data_length = (size_t)tcmu_cmd->dbi_cnt * blk_size;
+	bool zero_copy = false;
 
 	*scsi_err = TCM_NO_SENSE;
 
@@ -1044,7 +1209,22 @@ static int queue_cmd_ring(struct tcmu_cmd *tcmu_cmd, sense_reason_t *scsi_err)
 		return -1;
 	}
 
-	iov_cnt = tcmu_alloc_data_space(udev, tcmu_cmd, &iov_bidi_cnt);
+	if (!(se_cmd->se_cmd_flags & SCF_BIDI) && se_cmd->data_length &&
+	    IS_ALIGNED(se_cmd->data_length, PAGE_SIZE)) {
+		struct scatterlist *data_sg = se_cmd->t_data_sg, *sg;
+		unsigned int data_nents = se_cmd->t_data_nents;
+		int i;
+
+		for_each_sg(data_sg, sg, data_nents, i) {
+			if (!((!sg->offset || IS_ALIGNED(sg->offset, PAGE_SIZE)) &&
+			    IS_ALIGNED(sg->length, PAGE_SIZE)))
+				break;
+		}
+		if (i == data_nents)
+			zero_copy = true;
+	}
+
+	iov_cnt = tcmu_alloc_data_space(udev, tcmu_cmd, &iov_bidi_cnt, zero_copy);
 	if (iov_cnt < 0)
 		goto free_and_queue;
 
@@ -1093,7 +1273,7 @@ static int queue_cmd_ring(struct tcmu_cmd *tcmu_cmd, sense_reason_t *scsi_err)
 	tcmu_cmd_reset_dbi_cur(tcmu_cmd);
 	iov = &entry->req.iov[0];
 
-	if (se_cmd->data_direction == DMA_TO_DEVICE ||
+	if (((se_cmd->data_direction == DMA_TO_DEVICE) && !zero_copy) ||
 	    se_cmd->se_cmd_flags & SCF_BIDI)
 		scatter_data_area(udev, tcmu_cmd, &iov);
 	else
@@ -1111,6 +1291,11 @@ static int queue_cmd_ring(struct tcmu_cmd *tcmu_cmd, sense_reason_t *scsi_err)
 	tcmu_setup_cmd_timer(tcmu_cmd, udev->cmd_time_out, &udev->cmd_timer);
 
 	entry->hdr.cmd_id = tcmu_cmd->cmd_id;
+	if (zero_copy) {
+		iov = &entry->req.iov[0];
+		tcmu_cmd_zerocopy_map(udev, tcmu_cmd, iov, entry->req.iov_cnt);
+		set_bit(TCMU_CMD_BIT_ZEROCOPY, &tcmu_cmd->flags);
+	}
 
 	tcmu_hdr_set_len(&entry->hdr.len_op, command_size);
 
@@ -1366,7 +1551,10 @@ static bool tcmu_handle_completion(struct tcmu_cmd *cmd,
 		else
 			se_cmd->se_cmd_flags |= SCF_TREAT_READ_AS_NORMAL;
 	}
-	if (se_cmd->se_cmd_flags & SCF_BIDI) {
+
+	if (test_bit(TCMU_CMD_BIT_ZEROCOPY, &cmd->flags)) {
+		tcmu_cmd_zerocopy_unmap(cmd);
+	} else if (se_cmd->se_cmd_flags & SCF_BIDI) {
 		/* Get Data-In buffer before clean up */
 		gather_data_area(udev, cmd, true, read_len);
 	} else if (se_cmd->data_direction == DMA_FROM_DEVICE) {
@@ -1520,6 +1708,8 @@ static void tcmu_check_expired_ring_cmd(struct tcmu_cmd *cmd)
 	if (!time_after_eq(jiffies, cmd->deadline))
 		return;
 
+	if (test_bit(TCMU_CMD_BIT_ZEROCOPY, &cmd->flags))
+		tcmu_cmd_zerocopy_unmap(cmd);
 	set_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags);
 	list_del_init(&cmd->queue_entry);
 	se_cmd = cmd->se_cmd;
@@ -1618,6 +1808,8 @@ static struct se_device *tcmu_alloc_device(struct se_hba *hba, const char *name)
 	udev->data_pages_per_blk = DATA_PAGES_PER_BLK_DEF;
 	udev->max_blocks = DATA_AREA_PAGES_DEF / udev->data_pages_per_blk;
 	udev->data_area_mb = TCMU_PAGES_TO_MBS(DATA_AREA_PAGES_DEF);
+	udev->zc_max_blocks = ZC_DATA_AREA_PAGES_DEF / udev->data_pages_per_blk;
+	udev->zc_data_area_mb = TCMU_PAGES_TO_MBS(ZC_DATA_AREA_PAGES_DEF);
 
 	mutex_init(&udev->cmdr_lock);
 
@@ -1841,6 +2033,9 @@ static void tcmu_vma_open(struct vm_area_struct *vma)
 
 	pr_debug("vma_open\n");
 
+	udev->vma_vm_mm = vma->vm_mm;
+	udev->vma = vma;
+	mmgrab(udev->vma_vm_mm);
 	kref_get(&udev->kref);
 }
 
@@ -1850,6 +2045,10 @@ static void tcmu_vma_close(struct vm_area_struct *vma)
 
 	pr_debug("vma_close\n");
 
+	mmdrop(udev->vma_vm_mm);
+	udev->vma_vm_mm = NULL;
+	udev->vma = NULL;
+
 	/* release ref from tcmu_vma_open */
 	kref_put(&udev->kref, tcmu_dev_kref_release);
 }
@@ -1901,7 +2100,7 @@ static int tcmu_mmap(struct uio_info *info, struct vm_area_struct *vma)
 {
 	struct tcmu_dev *udev = container_of(info, struct tcmu_dev, uio_info);
 
-	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
+	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP | VM_MIXEDMAP;
 	vma->vm_ops = &tcmu_vm_ops;
 
 	vma->vm_private_data = udev;
@@ -2172,7 +2371,7 @@ static int tcmu_configure_device(struct se_device *dev)
 	struct tcmu_dev *udev = TCMU_DEV(dev);
 	struct uio_info *info;
 	struct tcmu_mailbox *mb;
-	size_t data_size;
+	size_t data_size, zc_data_size;
 	int ret = 0;
 
 	ret = tcmu_update_uio_info(udev);
@@ -2183,8 +2382,9 @@ static int tcmu_configure_device(struct se_device *dev)
 
 	mutex_lock(&udev->cmdr_lock);
 	udev->data_bitmap = bitmap_zalloc(udev->max_blocks, GFP_KERNEL);
+	udev->zc_data_bitmap = bitmap_zalloc(udev->zc_max_blocks, GFP_KERNEL);
 	mutex_unlock(&udev->cmdr_lock);
-	if (!udev->data_bitmap) {
+	if (!udev->data_bitmap || !udev->zc_data_bitmap) {
 		ret = -ENOMEM;
 		goto err_bitmap_alloc;
 	}
@@ -2201,7 +2401,8 @@ static int tcmu_configure_device(struct se_device *dev)
 	udev->cmdr_size = CMDR_SIZE;
 	udev->data_off = MB_CMDR_SIZE;
 	data_size = TCMU_MBS_TO_PAGES(udev->data_area_mb) << PAGE_SHIFT;
-	udev->mmap_pages = (data_size + MB_CMDR_SIZE) >> PAGE_SHIFT;
+	zc_data_size = TCMU_MBS_TO_PAGES(udev->zc_data_area_mb) << PAGE_SHIFT;
+	udev->mmap_pages = (data_size + zc_data_size + MB_CMDR_SIZE) >> PAGE_SHIFT;
 	udev->data_blk_size = udev->data_pages_per_blk * PAGE_SIZE;
 	udev->dbi_thresh = 0; /* Default in Idle state */
 
@@ -2221,7 +2422,7 @@ static int tcmu_configure_device(struct se_device *dev)
 
 	info->mem[0].name = "tcm-user command & data buffer";
 	info->mem[0].addr = (phys_addr_t)(uintptr_t)udev->mb_addr;
-	info->mem[0].size = data_size + MB_CMDR_SIZE;
+	info->mem[0].size = data_size + zc_data_size + MB_CMDR_SIZE;
 	info->mem[0].memtype = UIO_MEM_NONE;
 
 	info->irqcontrol = tcmu_irqcontrol;
-- 
2.14.4.44.g2045bb6