ext4: Support for synchronous DAX faults

We return IOMAP_F_DIRTY flag from ext4_iomap_begin() when asked to
prepare blocks for writing and the inode has some uncommitted metadata
changes. In the fault handler ext4_dax_fault() we then detect this case
(through VM_FAULT_NEEDDSYNC return value) and call helper
dax_finish_sync_fault() to flush metadata changes and insert page table
entry. Note that this will also dirty corresponding radix tree entry
which is what we want - fsync(2) will still provide data integrity
guarantees for applications not using userspace flushing. And
applications using userspace flushing can avoid calling fsync(2) and
thus avoid the performance overhead.

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 208adfc..08a1d1a 100644 (file)
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -26,6 +26,7 @@
 #include <linux/quotaops.h>
 #include <linux/pagevec.h>
 #include <linux/uio.h>
+#include <linux/mman.h>
 #include "ext4.h"
 #include "ext4_jbd2.h"
 #include "xattr.h"
@@ -295,6 +296,7 @@ static int ext4_dax_huge_fault(struct vm_fault *vmf,
         */
        bool write = (vmf->flags & FAULT_FLAG_WRITE) &&
                (vmf->vma->vm_flags & VM_SHARED);
+       pfn_t pfn;
 
        if (write) {
                sb_start_pagefault(sb);
@@ -310,9 +312,12 @@ static int ext4_dax_huge_fault(struct vm_fault *vmf,
        } else {
                down_read(&EXT4_I(inode)->i_mmap_sem);
        }
-       result = dax_iomap_fault(vmf, pe_size, NULL, &ext4_iomap_ops);
+       result = dax_iomap_fault(vmf, pe_size, &pfn, &ext4_iomap_ops);
        if (write) {
                ext4_journal_stop(handle);
+               /* Handling synchronous page fault? */
+               if (result & VM_FAULT_NEEDDSYNC)
+                       result = dax_finish_sync_fault(vmf, pe_size, pfn);
                up_read(&EXT4_I(inode)->i_mmap_sem);
                sb_end_pagefault(sb);
        } else {
@@ -350,6 +355,13 @@ static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
        if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
                return -EIO;
 
+       /*
+        * We don't support synchronous mappings for non-DAX files. At least
+        * until someone comes with a sensible use case.
+        */
+       if (!IS_DAX(file_inode(file)) && (vma->vm_flags & VM_SYNC))
+               return -EOPNOTSUPP;
+
        file_accessed(file);
        if (IS_DAX(file_inode(file))) {
                vma->vm_ops = &ext4_dax_vm_ops;
@@ -719,6 +731,7 @@ const struct file_operations ext4_file_operations = {
        .compat_ioctl   = ext4_compat_ioctl,
 #endif
        .mmap           = ext4_file_mmap,
+       .mmap_supported_flags = MAP_SYNC,
        .open           = ext4_file_open,
        .release        = ext4_release_file,
        .fsync          = ext4_sync_file,

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 31db875..13a1989 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3394,6 +3394,19 @@ static int ext4_releasepage(struct page *page, gfp_t wait)
 }
 
 #ifdef CONFIG_FS_DAX
+static bool ext4_inode_datasync_dirty(struct inode *inode)
+{
+       journal_t *journal = EXT4_SB(inode->i_sb)->s_journal;
+
+       if (journal)
+               return !jbd2_transaction_committed(journal,
+                                       EXT4_I(inode)->i_datasync_tid);
+       /* Any metadata buffers to write? */
+       if (!list_empty(&inode->i_mapping->private_list))
+               return true;
+       return inode->i_state & I_DIRTY_DATASYNC;
+}
+
 static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
                            unsigned flags, struct iomap *iomap)
 {
@@ -3466,6 +3479,8 @@ retry:
        }
 
        iomap->flags = 0;
+       if ((flags & IOMAP_WRITE) && ext4_inode_datasync_dirty(inode))
+               iomap->flags |= IOMAP_F_DIRTY;
        iomap->bdev = inode->i_sb->s_bdev;
        iomap->dax_dev = sbi->s_daxdev;
        iomap->offset = first_block << blkbits;

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 7d5ef3b..fa8cde4 100644 (file)
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -738,6 +738,23 @@ int jbd2_log_wait_commit(journal_t *journal, tid_t tid)
        return err;
 }
 
+/* Return 1 when transaction with given tid has already committed. */
+int jbd2_transaction_committed(journal_t *journal, tid_t tid)
+{
+       int ret = 1;
+
+       read_lock(&journal->j_state_lock);
+       if (journal->j_running_transaction &&
+           journal->j_running_transaction->t_tid == tid)
+               ret = 0;
+       if (journal->j_committing_transaction &&
+           journal->j_committing_transaction->t_tid == tid)
+               ret = 0;
+       read_unlock(&journal->j_state_lock);
+       return ret;
+}
+EXPORT_SYMBOL(jbd2_transaction_committed);
+
 /*
  * When this function returns the transaction corresponding to tid
  * will be completed.  If the transaction has currently running, start

diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 606b6bc..296d1e0 100644 (file)
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -1367,6 +1367,7 @@ int jbd2_log_start_commit(journal_t *journal, tid_t tid);
 int __jbd2_log_start_commit(journal_t *journal, tid_t tid);
 int jbd2_journal_start_commit(journal_t *journal, tid_t *tid);
 int jbd2_log_wait_commit(journal_t *journal, tid_t tid);
+int jbd2_transaction_committed(journal_t *journal, tid_t tid);
 int jbd2_complete_transaction(journal_t *journal, tid_t tid);
 int jbd2_log_do_checkpoint(journal_t *journal);
 int jbd2_trans_will_send_data_barrier(journal_t *journal, tid_t tid);