erofs: dax support for non-tailpacking regular file

DAX is quite useful for some VM use cases in order to save guest
memory extremely with minimal lightweight EROFS.

In order to prepare for such use cases, add preliminary dax support
for non-tailpacking regular files for now.

Tested with the DRAM-emulated PMEM and the EROFS image generated by
"mkfs.erofs -Enoinline_data enwik9.fsdax.img enwik9"

Link: https://lore.kernel.org/r/20210805003601.183063-3-hsiangkao@linux.alibaba.com
Cc: nvdimm@lists.linux.dev
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

1 files changed, 40 insertions, 2 deletions

diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index 4158572c9e1e..fb2e554c861b 100644
--- a/fs/erofs/data.c
+++ b/fs/erofs/data.c
@@ -6,7 +6,7 @@
 #include "internal.h"
 #include <linux/prefetch.h>
 #include <linux/iomap.h>
-
+#include <linux/dax.h>
 #include <trace/events/erofs.h>
 
 static void erofs_readendio(struct bio *bio)
@@ -323,6 +323,7 @@ static int erofs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 		return ret;
 
 	iomap->bdev = inode->i_sb->s_bdev;
+	iomap->dax_dev = EROFS_I_SB(inode)->dax_dev;
 	iomap->offset = map.m_la;
 	iomap->length = map.m_llen;
 	iomap->flags = 0;
@@ -382,6 +383,10 @@ static ssize_t erofs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	if (!iov_iter_count(to))
 		return 0;
 
+#ifdef CONFIG_FS_DAX
+	if (IS_DAX(iocb->ki_filp->f_mapping->host))
+		return dax_iomap_rw(iocb, to, &erofs_iomap_ops);
+#endif
 	if (iocb->ki_flags & IOCB_DIRECT) {
 		int err = erofs_prepare_dio(iocb, to);
 
@@ -402,9 +407,42 @@ const struct address_space_operations erofs_raw_access_aops = {
 	.direct_IO = noop_direct_IO,
 };
 
+#ifdef CONFIG_FS_DAX
+static vm_fault_t erofs_dax_huge_fault(struct vm_fault *vmf,
+		enum page_entry_size pe_size)
+{
+	return dax_iomap_fault(vmf, pe_size, NULL, NULL, &erofs_iomap_ops);
+}
+
+static vm_fault_t erofs_dax_fault(struct vm_fault *vmf)
+{
+	return erofs_dax_huge_fault(vmf, PE_SIZE_PTE);
+}
+
+static const struct vm_operations_struct erofs_dax_vm_ops = {
+	.fault		= erofs_dax_fault,
+	.huge_fault	= erofs_dax_huge_fault,
+};
+
+static int erofs_file_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	if (!IS_DAX(file_inode(file)))
+		return generic_file_readonly_mmap(file, vma);
+
+	if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
+		return -EINVAL;
+
+	vma->vm_ops = &erofs_dax_vm_ops;
+	vma->vm_flags |= VM_HUGEPAGE;
+	return 0;
+}
+#else
+#define erofs_file_mmap	generic_file_readonly_mmap
+#endif
+
 const struct file_operations erofs_file_fops = {
 	.llseek		= generic_file_llseek,
 	.read_iter	= erofs_file_read_iter,
-	.mmap		= generic_file_readonly_mmap,
+	.mmap		= erofs_file_mmap,
 	.splice_read	= generic_file_splice_read,
 };