diff mbox series

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

Message ID 20210319015237.993880-3-ruansy.fnst@fujitsu.com (mailing list archive)
State Superseded
Headers show
Series fsdax,xfs: Add reflink&dedupe support for fsdax | expand

Commit Message

ruansy.fnst@fujitsu.com March 19, 2021, 1:52 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 | 291 +++++++++++++++++++++++++++----------------------------
 1 file changed, 145 insertions(+), 146 deletions(-)

Comments

Ritesh Harjani March 23, 2021, 3:48 p.m. UTC | #1
On 3/19/21 7:22 AM, 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 | 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;

shouldn't we use xa_index here for pos ?
(loff_t)xas->xa_index << 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;
> +	}

So now in case if mapping is not mapped, we always cause
VM_FAULT_SIGBUG. But earlier we were only doing WARN_ON_ONCE(1).
Can you pls help answer why the change in behavior?




> +
> +	err = dax_iomap_pfn(iomap, pos, size, &pfn);
> +	if (err)
> +		return dax_fault_return(err);

Same case here as well. This could return SIGBUS while earlier I am not 
sure why were we only returning FALLBACK?


> +
> +	entry = dax_insert_entry(xas, mapping, vmf, entry, pfn, 0,
> +				 write && !sync);

In dax_insert_entry() we are passing 0 as flags.
We should be passing DAX_PMD/DAX_PTE no?


> +
> +	if (sync)
> +		return dax_fault_synchronous_pfnp(pfnp, pfn);
> +


/* handle PMD case here */
> +	if (pmd)
> +		return vmf_insert_pfn_pmd(vmf, pfn, write);

/* handle PTE case here */
> +	if (write)
> +		return vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
> +	else
> +		return vmf_insert_mixed(vmf->vma, vmf->address, pfn);
> +}

It is easy to miss the return from if(pmd) case while reading.
A comment like above could be helpful for code review.


> +
>   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;
>   	}

It is much better if above accounting is also done in dax_fault_actor()
function itself. Then at the end of this function we need to just do
"return ret"  instead of "return ret | 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;
>   }


-ritesh
ruansy.fnst@fujitsu.com March 31, 2021, 3:57 a.m. UTC | #2
> -----Original Message-----
> From: Ritesh Harjani <riteshh@linux.ibm.com>
> Sent: Tuesday, March 23, 2021 11:48 PM
> Subject: Re: [PATCH v3 02/10] fsdax: Factor helper: dax_fault_actor()
> 
> 
> 
> On 3/19/21 7:22 AM, 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 | 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;
> 
> shouldn't we use xa_index here for pos ?
> (loff_t)xas->xa_index << PAGE_SHIFT;
Yes.
> 
> > +	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;
> > +	}
> 
> So now in case if mapping is not mapped, we always cause VM_FAULT_SIGBUG.
> But earlier we were only doing WARN_ON_ONCE(1).
> Can you pls help answer why the change in behavior?
> 

The behavior in PTE fault was always check the error code by dax_fault_return(error) after WARN_ON_ONCE(1).  So, I moved the dax_fault_return() into dax_fault_actor().  But I just found that, in PMD fault, it didn't do this check.  So, I think I should move dax_fault_return() outside the dax_fault_actor() to keep the previous logic.

> 
> 
> 
> > +
> > +	err = dax_iomap_pfn(iomap, pos, size, &pfn);
> > +	if (err)
> > +		return dax_fault_return(err);
> 
> Same case here as well. This could return SIGBUS while earlier I am not sure
> why were we only returning FALLBACK?
> 
Yes.  Thanks for pointing out.
> 
> > +
> > +	entry = dax_insert_entry(xas, mapping, vmf, entry, pfn, 0,
> > +				 write && !sync);
> 
> In dax_insert_entry() we are passing 0 as flags.
> We should be passing DAX_PMD/DAX_PTE no?
> 
My mistake.
> 
> > +
> > +	if (sync)
> > +		return dax_fault_synchronous_pfnp(pfnp, pfn);
> > +
> 
> 
> /* handle PMD case here */
> > +	if (pmd)
> > +		return vmf_insert_pfn_pmd(vmf, pfn, write);
> 
> /* handle PTE case here */
> > +	if (write)
> > +		return vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
> > +	else
> > +		return vmf_insert_mixed(vmf->vma, vmf->address, pfn);
> > +}
> 
> It is easy to miss the return from if(pmd) case while reading.
> A comment like above could be helpful for code review.
> 
> 
> > +
> >   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;
> >   	}
> 
> It is much better if above accounting is also done in dax_fault_actor()
> function itself. Then at the end of this function we need to just do
> "return ret"  instead of "return ret | major"
> 
Yes.


--
Thanks,
Ruan Shiyang.
> 
> >
> > - 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;
> >   }
> 
> 
> -ritesh
Christoph Hellwig April 2, 2021, 7:47 a.m. UTC | #3
> +		if (!pmd)
> +			return dax_load_hole(xas, mapping, &entry, vmf);
> +		else
> +			return dax_pmd_load_hole(xas, vmf, iomap, &entry);

> +	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);
> +}

No need for else statements after returning.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>
diff mbox series

Patch

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,