From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ross Zwisler Subject: Re: [PATCH 06/10] dax: provide an iomap based fault handler Date: Tue, 13 Sep 2016 17:10:39 -0600 Message-ID: <20160913231039.GF26002@linux.intel.com> References: <1473438884-674-1-git-send-email-hch@lst.de> <1473438884-674-7-git-send-email-hch@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1473438884-674-7-git-send-email-hch@lst.de> Sender: linux-fsdevel-owner@vger.kernel.org To: Christoph Hellwig Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-nvdimm@ml01.01.org List-Id: linux-nvdimm@lists.01.org On Fri, Sep 09, 2016 at 06:34:40PM +0200, Christoph Hellwig wrote: > Very similar to the existing dax_fault function, but instead of using > the get_block callback we rely on the iomap_ops vector from iomap.c. > That also avoids having to do two calls into the file system for write > faults. > > Signed-off-by: Christoph Hellwig > --- > fs/dax.c | 113 ++++++++++++++++++++++++++++++++++++++++++++++++++ > include/linux/iomap.h | 2 + > 2 files changed, 115 insertions(+) > > diff --git a/fs/dax.c b/fs/dax.c > index 57ad456..a170a94 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -1343,4 +1343,117 @@ iomap_dax_rw(struct kiocb *iocb, struct iov_iter *iter, > return done; > } > EXPORT_SYMBOL_GPL(iomap_dax_rw); > + > +/** > + * iomap_dax_fault - handle a page fault on a DAX file > + * @vma: The virtual memory area where the fault occurred > + * @vmf: The description of the fault > + * @ops: iomap ops passed from the file system > + * > + * When a page fault occurs, filesystems may call this helper in their fault > + * or mkwrite handler for DAX files. Sssumes the caller has done all the Assumes > + * necessary locking for the page fault to proceed successfully. > + */ > +int iomap_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf, > + struct iomap_ops *ops) > +{ > + struct address_space *mapping = vma->vm_file->f_mapping; > + struct inode *inode = mapping->host; > + unsigned long vaddr = (unsigned long)vmf->virtual_address; > + loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT; > + sector_t sector; > + struct iomap iomap = { 0 }; > + unsigned flags = 0; > + int error, major = 0; > + void *entry; > + > + /* > + * Check whether offset isn't beyond end of file now. Caller is supposed > + * to hold locks serializing us with truncate / punch hole so this is > + * a reliable test. > + */ > + if (pos >= i_size_read(inode)) > + return VM_FAULT_SIGBUS; > + > + entry = grab_mapping_entry(mapping, vmf->pgoff); > + if (IS_ERR(entry)) { > + error = PTR_ERR(entry); > + goto out; > + } > + > + if ((vmf->flags & FAULT_FLAG_WRITE) && !vmf->cow_page) > + flags |= IOMAP_WRITE; > + > + /* > + * Note that we don't bother to use iomap_apply here: DAX required > + * the file system block size to be equal the page size, which means > + * that we never have to deal with more than a single extent here. > + */ > + error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap); > + if (error) > + goto unlock_entry; > + if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) { > + error = -EIO; /* fs corruption? */ > + goto unlock_entry; > + } > + > + sector = iomap.blkno + (((pos & PAGE_MASK) - iomap.offset) >> 9); > + > + if (vmf->cow_page) { > + switch (iomap.type) { > + case IOMAP_HOLE: > + case IOMAP_UNWRITTEN: > + clear_user_highpage(vmf->cow_page, vaddr); > + break; > + case IOMAP_MAPPED: > + error = copy_user_dax(iomap.bdev, sector, PAGE_SIZE, > + vmf->cow_page, vaddr); > + break; > + default: > + WARN_ON_ONCE(1); > + error = -EIO; > + break; > + } > + > + if (error) > + goto unlock_entry; > + if (!radix_tree_exceptional_entry(entry)) { > + vmf->page = entry; > + return VM_FAULT_LOCKED; > + } > + vmf->entry = entry; > + return VM_FAULT_DAX_LOCKED; > + } > + > + switch (iomap.type) { > + case IOMAP_MAPPED: > + if (iomap.flags & IOMAP_F_NEW) { > + count_vm_event(PGMAJFAULT); > + mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT); > + major = VM_FAULT_MAJOR; > + } > + break; > + case IOMAP_UNWRITTEN: > + case IOMAP_HOLE: > + if (!(vmf->flags & FAULT_FLAG_WRITE)) > + return dax_load_hole(mapping, entry, vmf); > + default: > + WARN_ON_ONCE(1); > + error = -EIO; > + } > + > + /* Filesystem should not return unwritten buffers to us! */ This comment is above a WARN_ON_ONCE() that checks for unwritten buffers in dax_fault(), but that test isn't present in this code nor do we disallow unwritten buffers (apparently, based on the IOMAP_UNWRITTEN handling above). This comment should probably be removed. > + error = dax_insert_mapping(mapping, iomap.bdev, sector, PAGE_SIZE, > + &entry, vma, vmf); > +unlock_entry: If you stick a space in front of the labels (as is done in the rest of dax.c) it prevents future patches from using them at the beginning of hunks. Here's a patch adding a random space as an example: @@ -908,6 +908,7 @@ out: return VM_FAULT_OOM | major; /* -EBUSY is fine, somebody else faulted on the same PTE */ if ((error < 0) && (error != -EBUSY)) return VM_FAULT_SIGBUS | major; + return VM_FAULT_NOPAGE | major; } vs @@ -908,6 +908,7 @@ int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf, return VM_FAULT_OOM | major; /* -EBUSY is fine, somebody else faulted on the same PTE */ if ((error < 0) && (error != -EBUSY)) return VM_FAULT_SIGBUS | major; + return VM_FAULT_NOPAGE | major; } where 'out' is a label without a leading space in the first case and with a leading space in the second. With these few nits addressed: Reviewed-by: Ross Zwisler > + put_locked_mapping_entry(mapping, vmf->pgoff, entry); > +out: > + if (error == -ENOMEM) > + return VM_FAULT_OOM | major; > + /* -EBUSY is fine, somebody else faulted on the same PTE */ > + if (error < 0 && error != -EBUSY) > + return VM_FAULT_SIGBUS | major; > + return VM_FAULT_NOPAGE | major; > +} > +EXPORT_SYMBOL_GPL(iomap_dax_fault); > #endif /* CONFIG_FS_IOMAP */ > diff --git a/include/linux/iomap.h b/include/linux/iomap.h > index 3d5f785..a4ef953 100644 > --- a/include/linux/iomap.h > +++ b/include/linux/iomap.h > @@ -73,6 +73,8 @@ int iomap_truncate_page(struct inode *inode, loff_t pos, bool *did_zero, > struct iomap_ops *ops); > int iomap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf, > struct iomap_ops *ops); > +int iomap_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf, > + struct iomap_ops *ops); > int iomap_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo, > loff_t start, loff_t len, struct iomap_ops *ops); > > -- > 2.1.4 > > _______________________________________________ > Linux-nvdimm mailing list > Linux-nvdimm@lists.01.org > https://lists.01.org/mailman/listinfo/linux-nvdimm