Re: [PATCH v2 2/3] erofs: dax support for non-tailpacking regular file
From: Chao Yu
Date: Wed Aug 04 2021 - 03:14:47 EST
On 2021/7/31 3:46, Gao Xiang wrote:
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"
Cc: nvdimm@xxxxxxxxxxxxxxx
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
---
fs/erofs/data.c | 42 +++++++++++++++++++++++++++++--
fs/erofs/inode.c | 4 +++
fs/erofs/internal.h | 3 +++
fs/erofs/super.c | 60 +++++++++++++++++++++++++++++++++++++++++++--
4 files changed, 105 insertions(+), 4 deletions(-)
diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index 1f97151a9f90..911521293b20 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);
@@ -410,9 +415,42 @@ 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,
};
diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
index 00edb7562fea..e875fba18159 100644
--- a/fs/erofs/inode.c
+++ b/fs/erofs/inode.c
@@ -174,6 +174,10 @@ static struct page *erofs_read_inode(struct inode *inode,
inode->i_mtime.tv_nsec = inode->i_ctime.tv_nsec;
inode->i_atime.tv_nsec = inode->i_ctime.tv_nsec;
+ inode->i_flags &= ~S_DAX;
+ if (test_opt(&sbi->ctx, DAX_ALWAYS) && S_ISREG(inode->i_mode) &&
+ vi->datalayout == EROFS_INODE_FLAT_PLAIN)
+ inode->i_flags |= S_DAX;
if (!nblks)
/* measure inode.i_blocks as generic filesystems */
inode->i_blocks = roundup(inode->i_size, EROFS_BLKSIZ) >> 9;
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 2669c785d548..7c9abfc93109 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -83,6 +83,7 @@ struct erofs_sb_info {
struct erofs_sb_lz4_info lz4;
#endif /* CONFIG_EROFS_FS_ZIP */
+ struct dax_device *dax_dev;
u32 blocks;
u32 meta_blkaddr;
#ifdef CONFIG_EROFS_FS_XATTR
@@ -115,6 +116,8 @@ struct erofs_sb_info {
/* Mount flags set via mount options or defaults */
#define EROFS_MOUNT_XATTR_USER 0x00000010
#define EROFS_MOUNT_POSIX_ACL 0x00000020
+#define EROFS_MOUNT_DAX_ALWAYS 0x00000040
+#define EROFS_MOUNT_DAX_NEVER 0x00000080
#define clear_opt(ctx, option) ((ctx)->mount_opt &= ~EROFS_MOUNT_##option)
#define set_opt(ctx, option) ((ctx)->mount_opt |= EROFS_MOUNT_##option)
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 8fc6c04b54f4..d5b110fd365d 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -11,6 +11,7 @@
#include <linux/crc32c.h>
#include <linux/fs_context.h>
#include <linux/fs_parser.h>
+#include <linux/dax.h>
#include "xattr.h"
#define CREATE_TRACE_POINTS
@@ -355,6 +356,8 @@ enum {
Opt_user_xattr,
Opt_acl,
Opt_cache_strategy,
+ Opt_dax,
+ Opt_dax_enum,
We need to update doc for those new dax mount options.
Opt_err
};
@@ -365,14 +368,47 @@ static const struct constant_table erofs_param_cache_strategy[] = {
{}
};
+static const struct constant_table erofs_dax_param_enums[] = {
+ {"always", EROFS_MOUNT_DAX_ALWAYS},
+ {"never", EROFS_MOUNT_DAX_NEVER},
+ {}
+};
+
static const struct fs_parameter_spec erofs_fs_parameters[] = {
fsparam_flag_no("user_xattr", Opt_user_xattr),
fsparam_flag_no("acl", Opt_acl),
fsparam_enum("cache_strategy", Opt_cache_strategy,
erofs_param_cache_strategy),
+ fsparam_flag("dax", Opt_dax),
+ fsparam_enum("dax", Opt_dax_enum, erofs_dax_param_enums),
{}
};
+static bool erofs_fc_set_dax_mode(struct fs_context *fc, unsigned int mode)
+{
+#ifdef CONFIG_FS_DAX
+ struct erofs_fs_context *ctx = fc->fs_private;
+
+ switch (mode) {
+ case EROFS_MOUNT_DAX_ALWAYS:
+ warnfc(fc, "DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
+ set_opt(ctx, DAX_ALWAYS);
+ clear_opt(ctx, DAX_NEVER);
+ return true;
+ case EROFS_MOUNT_DAX_NEVER:
+ set_opt(ctx, DAX_NEVER);
+ clear_opt(ctx, DAX_ALWAYS);
+ return true;
+ default:
+ DBG_BUGON(1);
+ return false;
+ }
+#else
+ errorfc(fc, "dax options not supported");
+ return false;
+#endif
+}
+
static int erofs_fc_parse_param(struct fs_context *fc,
struct fs_parameter *param)
{
@@ -412,6 +448,14 @@ static int erofs_fc_parse_param(struct fs_context *fc,
errorfc(fc, "compression not supported, cache_strategy ignored");
#endif
break;
+ case Opt_dax:
+ if (!erofs_fc_set_dax_mode(fc, EROFS_MOUNT_DAX_ALWAYS))
+ return -EINVAL;
+ break;
+ case Opt_dax_enum:
+ if (!erofs_fc_set_dax_mode(fc, result.uint_32))
+ return -EINVAL;
+ break;
default:
return -ENOPARAM;
}
@@ -496,10 +540,16 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
return -ENOMEM;
sb->s_fs_info = sbi;
+ sbi->dax_dev = fs_dax_get_by_bdev(sb->s_bdev);
err = erofs_read_superblock(sb);
if (err)
return err;
+ if (test_opt(ctx, DAX_ALWAYS) &&
+ !bdev_dax_supported(sb->s_bdev, EROFS_BLKSIZ)) {
+ errorfc(fc, "DAX unsupported by block device. Turning off DAX.");
+ clear_opt(ctx, DAX_ALWAYS);
+ }
sb->s_flags |= SB_RDONLY | SB_NOATIME;
sb->s_maxbytes = MAX_LFS_FILESIZE;
sb->s_time_gran = 1;
@@ -609,6 +659,8 @@ static void erofs_kill_sb(struct super_block *sb)
sbi = EROFS_SB(sb);
if (!sbi)
return;
+ if (sbi->dax_dev)
+ fs_put_dax(sbi->dax_dev);
fs_put_dax(sbi->dax_dev);
Thanks,
kfree(sbi);
sb->s_fs_info = NULL;
}
@@ -711,8 +763,8 @@ static int erofs_statfs(struct dentry *dentry, struct kstatfs *buf)
static int erofs_show_options(struct seq_file *seq, struct dentry *root)
{
- struct erofs_sb_info *sbi __maybe_unused = EROFS_SB(root->d_sb);
- struct erofs_fs_context *ctx __maybe_unused = &sbi->ctx;
+ struct erofs_sb_info *sbi = EROFS_SB(root->d_sb);
+ struct erofs_fs_context *ctx = &sbi->ctx;
#ifdef CONFIG_EROFS_FS_XATTR
if (test_opt(ctx, XATTR_USER))
@@ -734,6 +786,10 @@ static int erofs_show_options(struct seq_file *seq, struct dentry *root)
else if (ctx->cache_strategy == EROFS_ZIP_CACHE_READAROUND)
seq_puts(seq, ",cache_strategy=readaround");
#endif
+ if (test_opt(ctx, DAX_ALWAYS))
+ seq_puts(seq, ",dax=always");
+ if (test_opt(ctx, DAX_NEVER))
+ seq_puts(seq, ",dax=never");
return 0;
}