diff mbox series

[v2,02/10] fsdax: Factor helper: dax_fault_actor()

Message ID 20210226002030.653855-3-ruansy.fnst@fujitsu.com (mailing list archive)
State Superseded, archived
Headers show
Series fsdax,xfs: Add reflink&dedupe support for fsdax | expand

Commit Message

Shiyang Ruan Feb. 26, 2021, 12:20 a.m. UTC 
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 | 211 ++++++++++++++++++++++++++++++-------------------------
 1 file changed, 117 insertions(+), 94 deletions(-)

Comments

Christoph Hellwig March 3, 2021, 9:28 a.m. UTC | #1 
On Fri, Feb 26, 2021 at 08:20:22AM +0800, Shiyang Ruan wrote:
> 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 | 211 ++++++++++++++++++++++++++++++-------------------------
>  1 file changed, 117 insertions(+), 94 deletions(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 7031e4302b13..9dea1572868e 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -1289,6 +1289,93 @@ static int dax_fault_cow_page(struct vm_fault *vmf, struct iomap *iomap,
>  	return 0;
>  }
>  
> +static vm_fault_t dax_fault_insert_pfn(struct vm_fault *vmf, pfn_t pfn,
> +		bool pmd, bool write)
> +{
> +	vm_fault_t ret;
> +
> +	if (!pmd) {
> +		struct vm_area_struct *vma = vmf->vma;
> +		unsigned long address = vmf->address;
> +
> +		if (write)
> +			ret = vmf_insert_mixed_mkwrite(vma, address, pfn);
> +		else
> +			ret = vmf_insert_mixed(vma, address, pfn);
> +	} else
> +		ret = vmf_insert_pfn_pmd(vmf, pfn, write);

What about simplifying this a little bit more, something like:

	if (pmd)
		return vmf_insert_pfn_pmd(vmf, pfn, write);

	if (write)
		return vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
	return vmf_insert_mixed(vmf->vma, vmf->address, pfn);

also given that this only has a single user, why not keep open coding
it in the caller?

> +#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);
> +#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

Can we try to avoid the forward declaration?  Also is there a reason
dax_pmd_load_hole does not compile for the !CONFIG_FS_DAX_PMD case?
If it compiles fine we can just rely on IS_ENABLED() based dead code
elimination entirely.

> +	/* 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;
> +	}

Nit: I'd use a switch statement here for a clarity:

	switch (iomap->type) {
	case IOMAP_MAPPED:
		break;
	case IOMAP_UNWRITTEN:
	case IOMAP_HOLE:
		if (!write) {
			if (!pmd)
				return dax_load_hole(xas, mapping, &entry, vmf);
			return dax_pmd_load_hole(xas, vmf, iomap, &entry);
		}
		break;
	default:
		WARN_ON_ONCE(1);
		return VM_FAULT_SIGBUS;
	}


> +	err = dax_iomap_pfn(iomap, pos, size, &pfn);
> +	if (err)
> +		goto error_fault;
> +
> +	entry = dax_insert_entry(xas, mapping, vmf, entry, pfn, 0,
> +				 write && !sync);
> +
> +	if (sync)
> +		return dax_fault_synchronous_pfnp(pfnp, pfn);
> +
> +	ret = dax_fault_insert_pfn(vmf, pfn, pmd, write);
> +
> +error_fault:
> +	if (err)
> +		ret = dax_fault_return(err);
> +
> +	return ret;

It seems like the only place that sets err is the dax_iomap_pfn case
above.  So I'd move the dax_fault_return there, which then allows a direct
return for everyone else, including the open coded version of
dax_fault_insert_pfn.

I really like where this is going!
Shiyang Ruan March 12, 2021, 9:01 a.m. UTC | #2 
> > +	/* 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;
> > +	}
> 
> Nit: I'd use a switch statement here for a clarity:
> 
> 	switch (iomap->type) {
> 	case IOMAP_MAPPED:
> 		break;
> 	case IOMAP_UNWRITTEN:
> 	case IOMAP_HOLE:
> 		if (!write) {
> 			if (!pmd)
> 				return dax_load_hole(xas, mapping, &entry, vmf);
> 			return dax_pmd_load_hole(xas, vmf, iomap, &entry);
> 		}
> 		break;
> 	default:
> 		WARN_ON_ONCE(1);
> 		return VM_FAULT_SIGBUS;
> 	}
> 
Hi, Christoph

I did not use a switch-case here is because that I still have to introduce a 'goto' for CoW(Writing on IOMAP_UNWRITTEN and the two different iomap indicate that it is a CoW operation. Then goto IOMAP_MAPPED branch to do the data copy and pfn insertion.)  You said the 'goto' makes the code convoluted.  So, I avoided to use it and refactored this part into so much if-else, which looks similar in dax_iomap_actor().  So, what's your opinion now?


--
Thanks,
Ruan Shiyang.

> 
> > +	err = dax_iomap_pfn(iomap, pos, size, &pfn);
> > +	if (err)
> > +		goto error_fault;
> > +
> > +	entry = dax_insert_entry(xas, mapping, vmf, entry, pfn, 0,
> > +				 write && !sync);
> > +
> > +	if (sync)
> > +		return dax_fault_synchronous_pfnp(pfnp, pfn);
> > +
> > +	ret = dax_fault_insert_pfn(vmf, pfn, pmd, write);
> > +
> > +error_fault:
> > +	if (err)
> > +		ret = dax_fault_return(err);
> > +
> > +	return ret;
> 
> It seems like the only place that sets err is the dax_iomap_pfn case above.  So
> I'd move the dax_fault_return there, which then allows a direct return for
> everyone else, including the open coded version of dax_fault_insert_pfn.
> 
> I really like where this is going!
diff mbox series

Patch

diff --git a/fs/dax.c b/fs/dax.c
index 7031e4302b13..9dea1572868e 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1289,6 +1289,93 @@  static int dax_fault_cow_page(struct vm_fault *vmf, struct iomap *iomap,
 	return 0;
 }
 
+static vm_fault_t dax_fault_insert_pfn(struct vm_fault *vmf, pfn_t pfn,
+		bool pmd, bool write)
+{
+	vm_fault_t ret;
+
+	if (!pmd) {
+		struct vm_area_struct *vma = vmf->vma;
+		unsigned long address = vmf->address;
+
+		if (write)
+			ret = vmf_insert_mixed_mkwrite(vma, address, pfn);
+		else
+			ret = vmf_insert_mixed(vma, address, pfn);
+	} else
+		ret = vmf_insert_pfn_pmd(vmf, pfn, write);
+
+	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);
+#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
+
+/**
+ * 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);
+	vm_fault_t ret = 0;
+	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)
+		goto error_fault;
+
+	entry = dax_insert_entry(xas, mapping, vmf, entry, pfn, 0,
+				 write && !sync);
+
+	if (sync)
+		return dax_fault_synchronous_pfnp(pfnp, pfn);
+
+	ret = dax_fault_insert_pfn(vmf, pfn, pmd, write);
+
+error_fault:
+	if (err)
+		ret = dax_fault_return(err);
+
+	return ret;
+}
+
 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 +1383,14 @@  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 +1436,8 @@  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 +1447,19 @@  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;
 
@@ -1419,9 +1473,9 @@  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;
 }
@@ -1519,17 +1573,15 @@  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 +1593,7 @@  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 +1608,7 @@  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 +1620,7 @@  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 +1630,21 @@  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 +1652,18 @@  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,