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fs, dax: unify IOMAP_F_DIRTY read vs write handling policy in the dax core

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While reviewing whether MAP_SYNC should strengthen its current guarantee
of syncing writes from the initiating process to also include
third-party readers observing dirty metadata, Dave pointed out that the
check of IOMAP_WRITE is misplaced.

The policy of what to with IOMAP_F_DIRTY should be separated from the
generic filesystem mechanism of reporting dirty metadata. Move this
policy to the fs-dax core to simplify the per-filesystem iomap handlers,
and further centralize code that implements the MAP_SYNC policy. This
otherwise should not change behavior, it just makes it easier to change
behavior in the future.

Reviewed-by: Jan Kara <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Cc: Ross Zwisler <[email protected]>
Reported-by: Dave Chinner <[email protected]>
Signed-off-by: Dan Williams <[email protected]>
This commit is contained in:
Dan Williams 2017-11-13 16:38:44 -08:00
commit aaa422c4c3
3 changed files with 16 additions and 5 deletions
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15
fs/dax.c
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@ -1079,6 +1079,17 @@ static int dax_fault_return(int error)
return VM_FAULT_SIGBUS;
}
/*
* MAP_SYNC on a dax mapping guarantees dirty metadata is
* flushed on write-faults (non-cow), but not read-faults.
*/
static bool dax_fault_is_synchronous(unsigned long flags,
struct vm_area_struct *vma, struct iomap *iomap)
{
return (flags & IOMAP_WRITE) && (vma->vm_flags & VM_SYNC)
&& (iomap->flags & IOMAP_F_DIRTY);
}
static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
const struct iomap_ops *ops)
{
@ -1170,7 +1181,7 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
goto finish_iomap;
}
sync = (vma->vm_flags & VM_SYNC) && (iomap.flags & IOMAP_F_DIRTY);
sync = dax_fault_is_synchronous(flags, vma, &iomap);
switch (iomap.type) {
case IOMAP_MAPPED:
@ -1390,7 +1401,7 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
if (iomap.offset + iomap.length < pos + PMD_SIZE)
goto finish_iomap;
sync = (vma->vm_flags & VM_SYNC) && (iomap.flags & IOMAP_F_DIRTY);
sync = dax_fault_is_synchronous(iomap_flags, vma, &iomap);
switch (iomap.type) {
case IOMAP_MAPPED: