[PATCH v2 3/5] btrfs: send: allocate send buffer with alloc_page() and vmap() for v2

[Omar Sandoval <osandov@osandov.com>]

From: Omar Sandoval <osandov@fb.com>

For encoded writes, we need the raw pages for reading compressed data
directly via a bio. So, replace kvmalloc() with vmap() so we have access
to the raw pages. 144k is large enough that it usually gets allocated
with vmalloc(), anyways.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 fs/btrfs/send.c | 33 +++++++++++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 822458e6ffae..f04d815c5d16 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -81,6 +81,7 @@ struct send_ctx {
 	char *send_buf;
 	u32 send_size;
 	u32 send_max_size;
+	struct page **send_buf_pages;
 	u64 total_send_size;
 	u64 cmd_send_size[BTRFS_SEND_C_MAX + 1];
 	u64 flags;	/* 'flags' member of btrfs_ioctl_send_args is u64 */
@@ -7191,6 +7192,7 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 	struct btrfs_root *clone_root;
 	struct send_ctx *sctx = NULL;
 	u32 i;
+	u32 send_buf_num_pages = 0;
 	u64 *clone_sources_tmp = NULL;
 	int clone_sources_to_rollback = 0;
 	size_t alloc_size;
@@ -7271,10 +7273,28 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 	if (sctx->flags & BTRFS_SEND_FLAG_STREAM_V2) {
 		sctx->send_max_size = ALIGN(SZ_16K + BTRFS_MAX_COMPRESSED,
 					    PAGE_SIZE);
+		send_buf_num_pages = sctx->send_max_size >> PAGE_SHIFT;
+		sctx->send_buf_pages = kcalloc(send_buf_num_pages,
+					       sizeof(*sctx->send_buf_pages),
+					       GFP_KERNEL);
+		if (!sctx->send_buf_pages) {
+			send_buf_num_pages = 0;
+			ret = -ENOMEM;
+			goto out;
+		}
+		for (i = 0; i < send_buf_num_pages; i++) {
+			sctx->send_buf_pages[i] = alloc_page(GFP_KERNEL);
+			if (!sctx->send_buf_pages[i]) {
+				ret = -ENOMEM;
+				goto out;
+			}
+		}
+		sctx->send_buf = vmap(sctx->send_buf_pages, send_buf_num_pages,
+				      VM_MAP, PAGE_KERNEL);
 	} else {
 		sctx->send_max_size = BTRFS_SEND_BUF_SIZE_V1;
+		sctx->send_buf = kvmalloc(sctx->send_max_size, GFP_KERNEL);
 	}
-	sctx->send_buf = kvmalloc(sctx->send_max_size, GFP_KERNEL);
 	if (!sctx->send_buf) {
 		ret = -ENOMEM;
 		goto out;
@@ -7483,7 +7503,16 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 			fput(sctx->send_filp);
 
 		kvfree(sctx->clone_roots);
-		kvfree(sctx->send_buf);
+		if (sctx->flags & BTRFS_SEND_FLAG_STREAM_V2) {
+			vunmap(sctx->send_buf);
+			for (i = 0; i < send_buf_num_pages; i++) {
+				if (sctx->send_buf_pages[i])
+					__free_page(sctx->send_buf_pages[i]);
+			}
+			kfree(sctx->send_buf_pages);
+		} else {
+			kvfree(sctx->send_buf);
+		}
 
 		name_cache_free(sctx);
 
-- 
2.29.2