Commit b8a6176c authored by Jan Kara's avatar Jan Kara Committed by Dan Williams
Browse files

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: default avatarRoss Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
parent 497f6926

fs/ext4/file.c

+14 −1
Original line number Diff line number Diff line
@@ -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,

fs/ext4/inode.c

+15 −0
Original line number Diff line number Diff line
@@ -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;

fs/jbd2/journal.c

+17 −0
Original line number Diff line number Diff line
@@ -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

include/linux/jbd2.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

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