2016-11-24 09:46:34

by Jan Kara

Subject: [PATCH 4/6] dax: Finish fault completely when loading holes

The only case when we do not finish the page fault completely is when we
are loading hole pages into a radix tree. Avoid this special case and
finish the fault in that case as well inside the DAX fault handler. It
will allow us for easier iomap handling.

Signed-off-by: Jan Kara <[email protected]>
---
fs/dax.c | 27 ++++++++++++++++++---------
1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index ddf77ef2ca18..38f996976ebf 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -540,15 +540,16 @@ int dax_invalidate_clean_mapping_entry(struct address_space *mapping,
* otherwise it will simply fall out of the page cache under memory
* pressure without ever having been dirtied.
*/
-static int dax_load_hole(struct address_space *mapping, void *entry,
+static int dax_load_hole(struct address_space *mapping, void **entry,
struct vm_fault *vmf)
{
struct page *page;
+ int ret;

/* Hole page already exists? Return it... */
- if (!radix_tree_exceptional_entry(entry)) {
- vmf->page = entry;
- return VM_FAULT_LOCKED;
+ if (!radix_tree_exceptional_entry(*entry)) {
+ page = *entry;
+ goto out;
}

/* This will replace locked radix tree entry with a hole page */
@@ -556,8 +557,17 @@ static int dax_load_hole(struct address_space *mapping, void *entry,
vmf->gfp_mask | __GFP_ZERO);
if (!page)
return VM_FAULT_OOM;
+ out:
vmf->page = page;
- return VM_FAULT_LOCKED;
+ ret = finish_fault(vmf);
+ vmf->page = NULL;
+ *entry = page;
+ if (!ret) {
+ /* Grab reference for PTE that is now referencing the page */
+ get_page(page);
+ return VM_FAULT_NOPAGE;
+ }
+ return ret;
}

static int copy_user_dax(struct block_device *bdev, sector_t sector, size_t size,
@@ -1162,8 +1172,8 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
case IOMAP_UNWRITTEN:
case IOMAP_HOLE:
if (!(vmf->flags & FAULT_FLAG_WRITE)) {
- vmf_ret = dax_load_hole(mapping, entry, vmf);
- break;
+ vmf_ret = dax_load_hole(mapping, &entry, vmf);
+ goto finish_iomap;
}
/*FALLTHRU*/
default:
@@ -1184,8 +1194,7 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
}
}
unlock_entry:
- if (vmf_ret != VM_FAULT_LOCKED || error)
- put_locked_mapping_entry(mapping, vmf->pgoff, entry);
+ put_locked_mapping_entry(mapping, vmf->pgoff, entry);
out:
if (error == -ENOMEM)
return VM_FAULT_OOM | major;
--
2.6.6

2016-12-01 22:13:11

by Ross Zwisler

Subject: Re: [PATCH 4/6] dax: Finish fault completely when loading holes

On Thu, Nov 24, 2016 at 10:46:34AM +0100, Jan Kara wrote:
> The only case when we do not finish the page fault completely is when we
> are loading hole pages into a radix tree. Avoid this special case and
> finish the fault in that case as well inside the DAX fault handler. It
> will allow us for easier iomap handling.
>
> Signed-off-by: Jan Kara <[email protected]>

This seems correct to me.

Reviewed-by: Ross Zwisler <ross.zwisler-VuQAYsv1563Yd54FQh9/[email protected]>