From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C9923C282DD for ; Thu, 23 May 2019 14:04:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A5ABB2133D for ; Thu, 23 May 2019 14:04:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730790AbfEWOEs (ORCPT ); Thu, 23 May 2019 10:04:48 -0400 Received: from mx2.suse.de ([195.135.220.15]:53788 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730323AbfEWOEs (ORCPT ); Thu, 23 May 2019 10:04:48 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 5E988AD55; Thu, 23 May 2019 14:04:46 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id B02DA1E3C69; Thu, 23 May 2019 16:04:45 +0200 (CEST) Date: Thu, 23 May 2019 16:04:45 +0200 From: Jan Kara To: Goldwyn Rodrigues Cc: linux-btrfs@vger.kernel.org, kilobyte@angband.pl, linux-fsdevel@vger.kernel.org, jack@suse.cz, david@fromorbit.com, willy@infradead.org, hch@lst.de, darrick.wong@oracle.com, dsterba@suse.cz, nborisov@suse.com, linux-nvdimm@lists.01.org, Goldwyn Rodrigues Subject: Re: [PATCH 16/18] btrfs: Writeprotect mmap pages on snapshot Message-ID: <20190523140445.GD2949@quack2.suse.cz> References: <20190429172649.8288-1-rgoldwyn@suse.de> <20190429172649.8288-17-rgoldwyn@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190429172649.8288-17-rgoldwyn@suse.de> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Mon 29-04-19 12:26:47, Goldwyn Rodrigues wrote: > From: Goldwyn Rodrigues > > Inorder to make sure mmap'd files don't change after snapshot, > writeprotect the mmap pages on snapshot. This is done by performing > a data writeback on the pages (which simply mark the pages are > wrprotected). This way if the user process tries to access the memory > we will get another fault and we can perform a CoW. > > In order to accomplish this, we tag all CoW pages as > PAGECACHE_TAG_TOWRITE, and add the mmapd inode in delalloc_inodes. > During snapshot, it starts writeback of all delalloc'd inodes and > here we perform a data writeback. We don't want to keep the inodes > in delalloc_inodes until it umount (WARN_ON), so we remove it > during inode evictions. > > Signed-off-by: Goldwyn Rodrigues OK, so here you use PAGECACHE_TAG_TOWRITE. But why is not PAGECACHE_TAG_DIRTY enough for you? Also why isn't the same needed also for normal non-DAX inodes? There you also need to trigger CoW on mmap write so I just don't see the difference... Honza > --- > fs/btrfs/ctree.h | 3 ++- > fs/btrfs/dax.c | 7 +++++++ > fs/btrfs/inode.c | 13 ++++++++++++- > 3 files changed, 21 insertions(+), 2 deletions(-) > > diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h > index ee1ed18f8b3c..d1b70f24adeb 100644 > --- a/fs/btrfs/ctree.h > +++ b/fs/btrfs/ctree.h > @@ -3252,7 +3252,8 @@ int btrfs_create_subvol_root(struct btrfs_trans_handle *trans, > struct btrfs_root *new_root, > struct btrfs_root *parent_root, > u64 new_dirid); > - void btrfs_set_delalloc_extent(struct inode *inode, struct extent_state *state, > +void btrfs_add_delalloc_inodes(struct btrfs_root *root, struct inode *inode); > +void btrfs_set_delalloc_extent(struct inode *inode, struct extent_state *state, > unsigned *bits); > void btrfs_clear_delalloc_extent(struct inode *inode, > struct extent_state *state, unsigned *bits); > diff --git a/fs/btrfs/dax.c b/fs/btrfs/dax.c > index bf2ddac5b5a1..20ec2ec49c68 100644 > --- a/fs/btrfs/dax.c > +++ b/fs/btrfs/dax.c > @@ -222,10 +222,17 @@ vm_fault_t btrfs_dax_fault(struct vm_fault *vmf) > { > vm_fault_t ret; > pfn_t pfn; > + struct inode *inode = file_inode(vmf->vma->vm_file); > + struct btrfs_inode *binode = BTRFS_I(inode); > ret = dax_iomap_fault(vmf, PE_SIZE_PTE, &pfn, NULL, &btrfs_iomap_ops); > if (ret & VM_FAULT_NEEDDSYNC) > ret = dax_finish_sync_fault(vmf, PE_SIZE_PTE, pfn); > > + /* Insert into delalloc so we get writeback calls on snapshots */ > + if (vmf->flags & FAULT_FLAG_WRITE && > + !test_bit(BTRFS_INODE_IN_DELALLOC_LIST, &binode->runtime_flags)) > + btrfs_add_delalloc_inodes(binode->root, inode); > + > return ret; > } > > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c > index 7e88280a2c3b..e98fb512e1ca 100644 > --- a/fs/btrfs/inode.c > +++ b/fs/btrfs/inode.c > @@ -1713,7 +1713,7 @@ void btrfs_merge_delalloc_extent(struct inode *inode, struct extent_state *new, > spin_unlock(&BTRFS_I(inode)->lock); > } > > -static void btrfs_add_delalloc_inodes(struct btrfs_root *root, > +void btrfs_add_delalloc_inodes(struct btrfs_root *root, > struct inode *inode) > { > struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); > @@ -5358,12 +5358,17 @@ void btrfs_evict_inode(struct inode *inode) > { > struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); > struct btrfs_trans_handle *trans; > + struct btrfs_inode *binode = BTRFS_I(inode); > struct btrfs_root *root = BTRFS_I(inode)->root; > struct btrfs_block_rsv *rsv; > int ret; > > trace_btrfs_inode_evict(inode); > > + if (IS_DAX(inode) > + && test_bit(BTRFS_INODE_IN_DELALLOC_LIST, &binode->runtime_flags)) > + btrfs_del_delalloc_inode(root, binode); > + > if (!root) { > clear_inode(inode); > return; > @@ -8683,6 +8688,10 @@ static int btrfs_dax_writepages(struct address_space *mapping, > { > struct inode *inode = mapping->host; > struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); > + struct btrfs_inode *binode = BTRFS_I(inode); > + if ((wbc->sync_mode == WB_SYNC_ALL) && > + test_bit(BTRFS_INODE_IN_DELALLOC_LIST, &binode->runtime_flags)) > + btrfs_del_delalloc_inode(binode->root, binode); > return dax_writeback_mapping_range(mapping, fs_info->fs_devices->latest_bdev, > wbc); > } > @@ -9981,6 +9990,8 @@ static void btrfs_run_delalloc_work(struct btrfs_work *work) > delalloc_work = container_of(work, struct btrfs_delalloc_work, > work); > inode = delalloc_work->inode; > + if (IS_DAX(inode)) > + filemap_fdatawrite(inode->i_mapping); > filemap_flush(inode->i_mapping); > if (test_bit(BTRFS_INODE_HAS_ASYNC_EXTENT, > &BTRFS_I(inode)->runtime_flags)) > -- > 2.16.4 > -- Jan Kara SUSE Labs, CR