[PATCH v3 02/10] fsdax: Factor helper: dax_fault_actor()

Shiyang Ruan
2021-03-19T01:54:00Z

The core logic in the two dax page fault functions is similar. So, move
the logic into a common helper function. Also, to facilitate the
addition of new features, such as CoW, switch-case is no longer used to
handle different iomap types.

Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
---
fs/dax.c | 291 +++++++++++++++++++++++++++----------------------------
1 file changed, 145 insertions(+), 146 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 7031e4302b13..33ddad0f3091 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1053,6 +1053,66 @@ static vm_fault_t dax_load_hole(struct xa_state *xas,
return ret;
}

+#ifdef CONFIG_FS_DAX_PMD
+static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
+ struct iomap *iomap, void **entry)
+{
+ struct address_space *mapping = vmf->vma->vm_file->f_mapping;
+ unsigned long pmd_addr = vmf->address & PMD_MASK;
+ struct vm_area_struct *vma = vmf->vma;
+ struct inode *inode = mapping->host;
+ pgtable_t pgtable = NULL;
+ struct page *zero_page;
+ spinlock_t *ptl;
+ pmd_t pmd_entry;
+ pfn_t pfn;
+
+ zero_page = mm_get_huge_zero_page(vmf->vma->vm_mm);
+
+ if (unlikely(!zero_page))
+ goto fallback;
+
+ pfn = page_to_pfn_t(zero_page);
+ *entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,
+ DAX_PMD | DAX_ZERO_PAGE, false);
+
+ if (arch_needs_pgtable_deposit()) {
+ pgtable = pte_alloc_one(vma->vm_mm);
+ if (!pgtable)
+ return VM_FAULT_OOM;
+ }
+
+ ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
+ if (!pmd_none(*(vmf->pmd))) {
+ spin_unlock(ptl);
+ goto fallback;
+ }
+
+ if (pgtable) {
+ pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
+ mm_inc_nr_ptes(vma->vm_mm);
+ }
+ pmd_entry = mk_pmd(zero_page, vmf->vma->vm_page_prot);
+ pmd_entry = pmd_mkhuge(pmd_entry);
+ set_pmd_at(vmf->vma->vm_mm, pmd_addr, vmf->pmd, pmd_entry);
+ spin_unlock(ptl);
+ trace_dax_pmd_load_hole(inode, vmf, zero_page, *entry);
+ return VM_FAULT_NOPAGE;
+
+fallback:
+ if (pgtable)
+ pte_free(vma->vm_mm, pgtable);
+ trace_dax_pmd_load_hole_fallback(inode, vmf, zero_page, *entry);
+ return VM_FAULT_FALLBACK;
+}
+#else
+static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
+ struct iomap *iomap, void **entry)
+{
+ return VM_FAULT_FALLBACK;
+}
+#endif /* CONFIG_FS_DAX_PMD */
+
s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
{
sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
@@ -1289,6 +1349,61 @@ static int dax_fault_cow_page(struct vm_fault *vmf, struct iomap *iomap,
return 0;
}

+/**
+ * dax_fault_actor - Common actor to handle pfn insertion in PTE/PMD fault.
+ * @vmf: vm fault instance
+ * @pfnp: pfn to be returned
+ * @xas: the dax mapping tree of a file
+ * @entry: an unlocked dax entry to be inserted
+ * @pmd: distinguish whether it is a pmd fault
+ * @flags: iomap flags
+ * @iomap: from iomap_begin()
+ * @srcmap: from iomap_begin(), not equal to iomap if it is a CoW
+ */
+static vm_fault_t dax_fault_actor(struct vm_fault *vmf, pfn_t *pfnp,
+ struct xa_state *xas, void *entry, bool pmd, unsigned int flags,
+ struct iomap *iomap, struct iomap *srcmap)
+{
+ struct address_space *mapping = vmf->vma->vm_file->f_mapping;
+ size_t size = pmd ? PMD_SIZE : PAGE_SIZE;
+ loff_t pos = (loff_t)xas->xa_offset << PAGE_SHIFT;
+ bool write = vmf->flags & FAULT_FLAG_WRITE;
+ bool sync = dax_fault_is_synchronous(flags, vmf->vma, iomap);
+ int err = 0;
+ pfn_t pfn;
+
+ /* if we are reading UNWRITTEN and HOLE, return a hole. */
+ if (!write &&
+ (iomap->type == IOMAP_UNWRITTEN || iomap->type == IOMAP_HOLE)) {
+ if (!pmd)
+ return dax_load_hole(xas, mapping, &entry, vmf);
+ else
+ return dax_pmd_load_hole(xas, vmf, iomap, &entry);
+ }
+
+ if (iomap->type != IOMAP_MAPPED) {
+ WARN_ON_ONCE(1);
+ return VM_FAULT_SIGBUS;
+ }
+
+ err = dax_iomap_pfn(iomap, pos, size, &pfn);
+ if (err)
+ return dax_fault_return(err);
+
+ entry = dax_insert_entry(xas, mapping, vmf, entry, pfn, 0,
+ write && !sync);
+
+ if (sync)
+ return dax_fault_synchronous_pfnp(pfnp, pfn);
+
+ if (pmd)
+ return vmf_insert_pfn_pmd(vmf, pfn, write);
+ if (write)
+ return vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
+ else
+ return vmf_insert_mixed(vmf->vma, vmf->address, pfn);
+}
+
static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
int *iomap_errp, const struct iomap_ops *ops)
{
@@ -1296,17 +1411,14 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
struct address_space *mapping = vma->vm_file->f_mapping;
XA_STATE(xas, &mapping->i_pages, vmf->pgoff);
struct inode *inode = mapping->host;
- unsigned long vaddr = vmf->address;
loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT;
struct iomap iomap = { .type = IOMAP_HOLE };
struct iomap srcmap = { .type = IOMAP_HOLE };
unsigned flags = IOMAP_FAULT;
int error, major = 0;
bool write = vmf->flags & FAULT_FLAG_WRITE;
- bool sync;
vm_fault_t ret = 0;
void *entry;
- pfn_t pfn;

trace_dax_pte_fault(inode, vmf, ret);
/*
@@ -1352,8 +1464,8 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
goto unlock_entry;
}
if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) {
- error = -EIO; /* fs corruption? */
- goto error_finish_iomap;
+ ret = VM_FAULT_SIGBUS; /* fs corruption? */
+ goto finish_iomap;
}

if (vmf->cow_page) {
@@ -1363,49 +1475,19 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
goto finish_iomap;
}

- sync = dax_fault_is_synchronous(flags, vma, &iomap);
-
- switch (iomap.type) {
- case IOMAP_MAPPED:
- if (iomap.flags & IOMAP_F_NEW) {
- count_vm_event(PGMAJFAULT);
- count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
- major = VM_FAULT_MAJOR;
- }
- error = dax_iomap_pfn(&iomap, pos, PAGE_SIZE, &pfn);
- if (error < 0)
- goto error_finish_iomap;
-
- entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
- 0, write && !sync);
-
- if (sync) {
- ret = dax_fault_synchronous_pfnp(pfnp, pfn);
- goto finish_iomap;
- }
- trace_dax_insert_mapping(inode, vmf, entry);
- if (write)
- ret = vmf_insert_mixed_mkwrite(vma, vaddr, pfn);
- else
- ret = vmf_insert_mixed(vma, vaddr, pfn);
-
+ ret = dax_fault_actor(vmf, pfnp, &xas, entry, false, flags,
+ &iomap, &srcmap);
+ if (ret == VM_FAULT_SIGBUS)
goto finish_iomap;
- case IOMAP_UNWRITTEN:
- case IOMAP_HOLE:
- if (!write) {
- ret = dax_load_hole(&xas, mapping, &entry, vmf);
- goto finish_iomap;
- }
- fallthrough;
- default:
- WARN_ON_ONCE(1);
- error = -EIO;
- break;
+
+ /* read/write MAPPED, CoW UNWRITTEN */
+ if (iomap.flags & IOMAP_F_NEW) {
+ count_vm_event(PGMAJFAULT);
+ count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
+ major = VM_FAULT_MAJOR;
}

- error_finish_iomap:
- ret = dax_fault_return(error);
- finish_iomap:
+finish_iomap:
if (ops->iomap_end) {
int copied = PAGE_SIZE;

@@ -1419,66 +1501,14 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
*/
ops->iomap_end(inode, pos, PAGE_SIZE, copied, flags, &iomap);
}
- unlock_entry:
+unlock_entry:
dax_unlock_entry(&xas, entry);
- out:
+out:
trace_dax_pte_fault_done(inode, vmf, ret);
return ret | major;
}

#ifdef CONFIG_FS_DAX_PMD
-static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
- struct iomap *iomap, void **entry)
-{
- struct address_space *mapping = vmf->vma->vm_file->f_mapping;
- unsigned long pmd_addr = vmf->address & PMD_MASK;
- struct vm_area_struct *vma = vmf->vma;
- struct inode *inode = mapping->host;
- pgtable_t pgtable = NULL;
- struct page *zero_page;
- spinlock_t *ptl;
- pmd_t pmd_entry;
- pfn_t pfn;
-
- zero_page = mm_get_huge_zero_page(vmf->vma->vm_mm);
-
- if (unlikely(!zero_page))
- goto fallback;
-
- pfn = page_to_pfn_t(zero_page);
- *entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,
- DAX_PMD | DAX_ZERO_PAGE, false);
-
- if (arch_needs_pgtable_deposit()) {
- pgtable = pte_alloc_one(vma->vm_mm);
- if (!pgtable)
- return VM_FAULT_OOM;
- }
-
- ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
- if (!pmd_none(*(vmf->pmd))) {
- spin_unlock(ptl);
- goto fallback;
- }
-
- if (pgtable) {
- pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
- mm_inc_nr_ptes(vma->vm_mm);
- }
- pmd_entry = mk_pmd(zero_page, vmf->vma->vm_page_prot);
- pmd_entry = pmd_mkhuge(pmd_entry);
- set_pmd_at(vmf->vma->vm_mm, pmd_addr, vmf->pmd, pmd_entry);
- spin_unlock(ptl);
- trace_dax_pmd_load_hole(inode, vmf, zero_page, *entry);
- return VM_FAULT_NOPAGE;
-
-fallback:
- if (pgtable)
- pte_free(vma->vm_mm, pgtable);
- trace_dax_pmd_load_hole_fallback(inode, vmf, zero_page, *entry);
- return VM_FAULT_FALLBACK;
-}
-
static bool dax_fault_check_fallback(struct vm_fault *vmf, struct xa_state *xas,
pgoff_t max_pgoff)
{
@@ -1519,17 +1549,15 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
struct address_space *mapping = vma->vm_file->f_mapping;
XA_STATE_ORDER(xas, &mapping->i_pages, vmf->pgoff, PMD_ORDER);
bool write = vmf->flags & FAULT_FLAG_WRITE;
- bool sync;
- unsigned int iomap_flags = (write ? IOMAP_WRITE : 0) | IOMAP_FAULT;
+ unsigned int flags = (write ? IOMAP_WRITE : 0) | IOMAP_FAULT;
struct inode *inode = mapping->host;
- vm_fault_t result = VM_FAULT_FALLBACK;
+ vm_fault_t ret = VM_FAULT_FALLBACK;
struct iomap iomap = { .type = IOMAP_HOLE };
struct iomap srcmap = { .type = IOMAP_HOLE };
pgoff_t max_pgoff;
void *entry;
loff_t pos;
int error;
- pfn_t pfn;

/*
* Check whether offset isn't beyond end of file now. Caller is
@@ -1541,7 +1569,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
trace_dax_pmd_fault(inode, vmf, max_pgoff, 0);

if (xas.xa_index >= max_pgoff) {
- result = VM_FAULT_SIGBUS;
+ ret = VM_FAULT_SIGBUS;
goto out;
}

@@ -1556,7 +1584,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
*/
entry = grab_mapping_entry(&xas, mapping, PMD_ORDER);
if (xa_is_internal(entry)) {
- result = xa_to_internal(entry);
+ ret = xa_to_internal(entry);
goto fallback;
}

@@ -1568,7 +1596,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
*/
if (!pmd_none(*vmf->pmd) && !pmd_trans_huge(*vmf->pmd) &&
!pmd_devmap(*vmf->pmd)) {
- result = 0;
+ ret = 0;
goto unlock_entry;
}

@@ -1578,49 +1606,21 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
* to look up our filesystem block.
*/
pos = (loff_t)xas.xa_index << PAGE_SHIFT;
- error = ops->iomap_begin(inode, pos, PMD_SIZE, iomap_flags, &iomap,
- &srcmap);
+ error = ops->iomap_begin(inode, pos, PMD_SIZE, flags, &iomap, &srcmap);
if (error)
goto unlock_entry;

if (iomap.offset + iomap.length < pos + PMD_SIZE)
goto finish_iomap;

- sync = dax_fault_is_synchronous(iomap_flags, vma, &iomap);
-
- switch (iomap.type) {
- case IOMAP_MAPPED:
- error = dax_iomap_pfn(&iomap, pos, PMD_SIZE, &pfn);
- if (error < 0)
- goto finish_iomap;
+ ret = dax_fault_actor(vmf, pfnp, &xas, entry, true, flags,
+ &iomap, &srcmap);

- entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
- DAX_PMD, write && !sync);
-
- if (sync) {
- result = dax_fault_synchronous_pfnp(pfnp, pfn);
- goto finish_iomap;
- }
-
- trace_dax_pmd_insert_mapping(inode, vmf, PMD_SIZE, pfn, entry);
- result = vmf_insert_pfn_pmd(vmf, pfn, write);
- break;
- case IOMAP_UNWRITTEN:
- case IOMAP_HOLE:
- if (WARN_ON_ONCE(write))
- break;
- result = dax_pmd_load_hole(&xas, vmf, &iomap, &entry);
- break;
- default:
- WARN_ON_ONCE(1);
- break;
- }
-
- finish_iomap:
+finish_iomap:
if (ops->iomap_end) {
int copied = PMD_SIZE;

- if (result == VM_FAULT_FALLBACK)
+ if (ret == VM_FAULT_FALLBACK)
copied = 0;
/*
* The fault is done by now and there's no way back (other
@@ -1628,19 +1628,18 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
* Just ignore error from ->iomap_end since we cannot do much
* with it.
*/
- ops->iomap_end(inode, pos, PMD_SIZE, copied, iomap_flags,
- &iomap);
+ ops->iomap_end(inode, pos, PMD_SIZE, copied, flags, &iomap);
}
- unlock_entry:
+unlock_entry:
dax_unlock_entry(&xas, entry);
- fallback:
- if (result == VM_FAULT_FALLBACK) {
+fallback:
+ if (ret == VM_FAULT_FALLBACK) {
split_huge_pmd(vma, vmf->pmd, vmf->address);
count_vm_event(THP_FAULT_FALLBACK);
}
out:
- trace_dax_pmd_fault_done(inode, vmf, max_pgoff, result);
- return result;
+ trace_dax_pmd_fault_done(inode, vmf, max_pgoff, ret);
+ return ret;
}
#else
static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
--
2.30.1