From: Ross Zwisler Subject: Re: [PATCH 13/13] ext4: Support for synchronous DAX faults Date: Mon, 21 Aug 2017 13:19:48 -0600 Message-ID: <20170821191948.GD26220@linux.intel.com> References: <20170817160815.30466-1-jack@suse.cz> <20170817160815.30466-14-jack@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org, linux-nvdimm@lists.01.org, Andy Lutomirski , linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, Christoph Hellwig , Ross Zwisler , Dan Williams , Boaz Harrosh To: Jan Kara Return-path: Received: from mga03.intel.com ([134.134.136.65]:7396 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753600AbdHUTTu (ORCPT ); Mon, 21 Aug 2017 15:19:50 -0400 Content-Disposition: inline In-Reply-To: <20170817160815.30466-14-jack@suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu, Aug 17, 2017 at 06:08:15PM +0200, Jan Kara wrote: > We return IOMAP_F_NEEDDSYNC flag from ext4_iomap_begin() for a > synchronous write fault when inode has some uncommitted metadata > changes. In the fault handler ext4_dax_fault() we then detect this case, > call vfs_fsync_range() to make sure all metadata is committed, and call > dax_pfn_mkwrite() to mark PTE as writeable. Note that this will also Need to fix up the above line a little - s/dax_pfn_mkwrite/dax_insert_pfn_mkwrite/, and we insert the PTE as well as make it writeable. > dirty corresponding radix tree entry which is what we want - fsync(2) > will still provide data integrity guarantees for applications not using > userspace flushing. And applications using userspace flushing can avoid > calling fsync(2) and thus avoid the performance overhead. > > Signed-off-by: Jan Kara > --- > fs/ext4/file.c | 36 ++++++++++++++++++++++++++++++------ > fs/ext4/inode.c | 4 ++++ > fs/jbd2/journal.c | 17 +++++++++++++++++ > include/linux/jbd2.h | 1 + > 4 files changed, 52 insertions(+), 6 deletions(-) > > diff --git a/fs/ext4/file.c b/fs/ext4/file.c > index 850037e140d7..3765c4ed1368 100644 > --- a/fs/ext4/file.c > +++ b/fs/ext4/file.c > @@ -280,6 +280,7 @@ static int ext4_dax_huge_fault(struct vm_fault *vmf, > struct inode *inode = file_inode(vmf->vma->vm_file); > struct super_block *sb = inode->i_sb; > bool write = vmf->flags & FAULT_FLAG_WRITE; > + pfn_t pfn; > > if (write) { > sb_start_pagefault(sb); > @@ -287,16 +288,39 @@ static int ext4_dax_huge_fault(struct vm_fault *vmf, > down_read(&EXT4_I(inode)->i_mmap_sem); > handle = ext4_journal_start_sb(sb, EXT4_HT_WRITE_PAGE, > EXT4_DATA_TRANS_BLOCKS(sb)); > + if (IS_ERR(handle)) { > + up_read(&EXT4_I(inode)->i_mmap_sem); > + sb_end_pagefault(sb); > + return VM_FAULT_SIGBUS; > + } > } else { > down_read(&EXT4_I(inode)->i_mmap_sem); > } > - if (!IS_ERR(handle)) > - result = dax_iomap_fault(vmf, pe_size, &ext4_iomap_ops, NULL); > - else > - result = VM_FAULT_SIGBUS; > + result = dax_iomap_fault(vmf, pe_size, &ext4_iomap_ops, &pfn); > if (write) { > - if (!IS_ERR(handle)) > - ext4_journal_stop(handle); > + ext4_journal_stop(handle); > + /* Write fault but PFN mapped only RO? */ The above comment is out of date. > + if (result & VM_FAULT_NEEDDSYNC) { > + int err; > + loff_t start = ((loff_t)vmf->pgoff) << PAGE_SHIFT; > + size_t len = 0; > + > + if (pe_size == PE_SIZE_PTE) > + len = PAGE_SIZE; > +#ifdef CONFIG_FS_DAX_PMD > + else if (pe_size == PE_SIZE_PMD) > + len = HPAGE_PMD_SIZE; In fs/dax.c we always use PMD_SIZE. It looks like HPAGE_PMD_SIZE and PMD_SIZE are always the same (from include/linux/huge_mm.h, the only defintion of HPAGE_PMD_SIZE): #define HPAGE_PMD_SHIFT PMD_SHIFT #define HPAGE_PMD_SIZE ((1UL) << HPAGE_PMD_SHIFT) and AFAICT PMD_SIZE is defined to be 1<