RE: [PATCH v2 2/3] fsdax: Factor helper: dax_fault_actor()

> -----Original Message-----
> From: Darrick J. Wong <[email protected]>
> Sent: Friday, April 9, 2021 5:11 AM
> Subject: Re: [PATCH v2 2/3] fsdax: Factor helper: dax_fault_actor()
> 
> On Wed, Apr 07, 2021 at 09:38:22PM +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 <[email protected]>
> > Reviewed-by: Christoph Hellwig <[email protected]>
> > Reviewed-by: Ritesh Harjani <[email protected]>
> > ---
> >  fs/dax.c | 294
> > ++++++++++++++++++++++++++++---------------------------
> >  1 file changed, 148 insertions(+), 146 deletions(-)
> >
> > diff --git a/fs/dax.c b/fs/dax.c
> > index f843fb8fbbf1..6dea1fc11b46 100644
> > --- a/fs/dax.c
> > +++ b/fs/dax.c
> > @@ -1054,6 +1054,66 @@ 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); @@ -1291,6
> > +1351,64 @@ static vm_fault_t dax_fault_cow_page(struct vm_fault *vmf,
> struct iomap *iomap,
> >  	return ret;
> >  }
> >
> > +/**
> > + * 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_index << PAGE_SHIFT;
> > +	bool write = vmf->flags & FAULT_FLAG_WRITE;
> > +	bool sync = dax_fault_is_synchronous(flags, vmf->vma, iomap);
> > +	unsigned long entry_flags = pmd ? DAX_PMD : 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 pmd ? VM_FAULT_FALLBACK : VM_FAULT_SIGBUS;
> > +	}
> > +
> > +	err = dax_iomap_pfn(iomap, pos, size, &pfn);
> > +	if (err)
> > +		return pmd ? VM_FAULT_FALLBACK : dax_fault_return(err);
> > +
> > +	*entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn, entry_flags,
> > +				  write && !sync);
> > +
> > +	if (sync)
> > +		return dax_fault_synchronous_pfnp(pfnp, pfn);
> > +
> > +	/* insert PMD pfn */
> > +	if (pmd)
> > +		return vmf_insert_pfn_pmd(vmf, pfn, write);
> > +
> > +	/* insert PTE pfn */
> > +	if (write)
> > +		return vmf_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
> > +	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)  { @@
> > -1298,17 +1416,14 @@ 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;
> 
> Hmm, shouldn't major be vm_fault_t since we assign VM_FAULT_MAJOR to it?

Yes, I didn't notice it.  Will fix it in next version.


--
Thanks,
Ruan Shiyang.

> 
> --D
> 
> >  	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);
> >  	/*
> > @@ -1354,8 +1469,8 @@ 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 +1478,19 @@ 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 +1504,14 @@ 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 +1552,15 @@ 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 +1572,7 @@ 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 +1587,7 @@ 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 +1599,7 @@ 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 +1609,21 @@ 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 +1631,18 @@ 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,
> > --
> > 2.31.0
> >
> >
> >
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