Messages in this thread Patch in this message | | | Subject | Re: [PATCH v3 02/10] fsdax: Factor helper: dax_fault_actor() | From | Ritesh Harjani <> | Date | Tue, 23 Mar 2021 21:18:13 +0530 |
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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
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