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Message-ID: <OSAPR01MB2913ED1836FA6BB2C938C962F4739@OSAPR01MB2913.jpnprd01.prod.outlook.com>
Date: Fri, 9 Apr 2021 02:03:18 +0000
From: "ruansy.fnst@...itsu.com" <ruansy.fnst@...itsu.com>
To: "Darrick J. Wong" <djwong@...nel.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
"darrick.wong@...cle.com" <darrick.wong@...cle.com>,
"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
"willy@...radead.org" <willy@...radead.org>,
"jack@...e.cz" <jack@...e.cz>,
"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
"david@...morbit.com" <david@...morbit.com>,
"hch@....de" <hch@....de>, "rgoldwyn@...e.de" <rgoldwyn@...e.de>,
Ritesh Harjani <riteshh@...ux.ibm.com>
Subject: RE: [PATCH v2 2/3] fsdax: Factor helper: dax_fault_actor()
> -----Original Message-----
> From: Darrick J. Wong <djwong@...nel.org>
> 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 <ruansy.fnst@...itsu.com>
> > Reviewed-by: Christoph Hellwig <hch@....de>
> > Reviewed-by: Ritesh Harjani <riteshh@...ux.ibm.com>
> > ---
> > 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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