From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:43367 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S969091AbeE1Pxz (ORCPT ); Mon, 28 May 2018 11:53:55 -0400 Date: Mon, 28 May 2018 15:46:57 +0200 From: David Sterba To: Omar Sandoval Cc: linux-btrfs@vger.kernel.org, kernel-team@fb.com, linux-fsdevel@vger.kernel.org, Tejun Heo Subject: Re: [RFC PATCH v4 6/6] Btrfs: support swap files Message-ID: <20180528134657.GY6649@twin.jikos.cz> Reply-To: dsterba@suse.cz References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Thu, May 24, 2018 at 02:41:30PM -0700, Omar Sandoval wrote: > From: Omar Sandoval > > Implement the swap file a_ops on Btrfs. Activation needs to make sure > that the file can be used as a swap file, which currently means it must > be fully allocated as nocow with no compression on one device. It also > sets up the swap extents directly with add_swap_extent(), so export it. > > Signed-off-by: Omar Sandoval > --- > fs/btrfs/inode.c | 220 +++++++++++++++++++++++++++++++++++++++++++++++ > mm/swapfile.c | 1 + > 2 files changed, 221 insertions(+) > > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c > index 9228cb866115..6cca8529e307 100644 > --- a/fs/btrfs/inode.c > +++ b/fs/btrfs/inode.c > @@ -10526,6 +10526,224 @@ void btrfs_set_range_writeback(void *private_data, u64 start, u64 end) > } > } > > +struct btrfs_swap_info { > + u64 start; > + u64 block_start; > + u64 block_len; > + u64 lowest_ppage; > + u64 highest_ppage; > + unsigned long nr_pages; > + int nr_extents; > +}; > + > +static int btrfs_add_swap_extent(struct swap_info_struct *sis, > + struct btrfs_swap_info *bsi) > +{ > + unsigned long nr_pages; > + u64 first_ppage, first_ppage_reported, next_ppage; > + int ret; > + > + first_ppage = ALIGN(bsi->block_start, PAGE_SIZE) >> PAGE_SHIFT; > + next_ppage = ALIGN_DOWN(bsi->block_start + bsi->block_len, > + PAGE_SIZE) >> PAGE_SHIFT; > + > + if (first_ppage >= next_ppage) > + return 0; > + nr_pages = next_ppage - first_ppage; > + > + first_ppage_reported = first_ppage; > + if (bsi->start == 0) > + first_ppage_reported++; > + if (bsi->lowest_ppage > first_ppage_reported) > + bsi->lowest_ppage = first_ppage_reported; > + if (bsi->highest_ppage < (next_ppage - 1)) > + bsi->highest_ppage = next_ppage - 1; > + > + ret = add_swap_extent(sis, bsi->nr_pages, nr_pages, first_ppage); > + if (ret < 0) > + return ret; > + bsi->nr_extents += ret; > + bsi->nr_pages += nr_pages; > + return 0; > +} > + > +static int btrfs_swap_activate(struct swap_info_struct *sis, struct file *file, > + sector_t *span) > +{ > + struct inode *inode = file_inode(file); > + struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info; > + struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree; > + struct extent_state *cached_state = NULL; > + struct extent_map *em = NULL; > + struct btrfs_device *device = NULL; > + struct btrfs_swap_info bsi = { > + .lowest_ppage = (sector_t)-1ULL, > + }; > + int ret = 0; > + u64 isize = inode->i_size; > + u64 start; > + > + /* > + * The inode is locked, so these flags won't change after we check them. > + */ > + if (BTRFS_I(inode)->flags & BTRFS_INODE_COMPRESS) { > + btrfs_err(fs_info, "swapfile is compressed"); I'm not sure this is the right way to phrase the error message. I'd expect something like "swapfile cannot be compressed", but I also think I've seen the positive and negative elsewhere so there's no universal style to follow. > + return -EINVAL; > + } > + if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW)) { > + btrfs_err(fs_info, "swapfile is copy-on-write"); > + return -EINVAL; > + } > + > + /* > + * Balance or device remove/replace/resize can move stuff around from > + * under us. The EXCL_OP flag makes sure they aren't running/won't run > + * concurrently while we are mapping the swap extents, and the fs_info > + * nr_swapfiles counter prevents them from running while the swap file > + * is active and moving the extents. Note that this also prevents a > + * concurrent device add which isn't actually necessary, but it's not > + * really worth the trouble to allow it. > + */ > + if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) > + return -EBUSY; > + atomic_inc(&fs_info->nr_swapfiles); > + /* > + * Snapshots can create extents which require COW even if NODATACOW is > + * set. We use this counter to prevent snapshots. We must increment it > + * before walking the extents because we don't want a concurrent > + * snapshot to run after we've already checked the extents. > + */ > + atomic_inc(&BTRFS_I(inode)->root->nr_swapfiles); > + > + lock_extent_bits(io_tree, 0, isize - 1, &cached_state); > + start = 0; > + while (start < isize) { > + u64 end, logical_block_start, physical_block_start; > + u64 len = isize - start; > + > + em = btrfs_get_extent(BTRFS_I(inode), NULL, 0, start, len, 0); > + if (IS_ERR(em)) { > + ret = PTR_ERR(em); > + goto out; > + } > + end = extent_map_end(em); > + > + if (em->block_start == EXTENT_MAP_HOLE) { > + btrfs_err(fs_info, "swapfile has holes"); > + ret = -EINVAL; > + goto out; > + } > + if (em->block_start == EXTENT_MAP_INLINE) { > + /* > + * It's unlikely we'll ever actually find ourselves > + * here, as a file small enough to fit inline won't be > + * big enough to store more than the swap header, but in > + * case something changes in the future, let's catch it > + * here rather than later. > + */ > + btrfs_err(fs_info, "swapfile is inline"); > + ret = -EINVAL; > + goto out; > + } > + if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags)) { > + btrfs_err(fs_info, "swapfile is compressed"); > + ret = -EINVAL; > + goto out; > + } > + > + logical_block_start = em->block_start + (start - em->start); > + len = min(len, em->len - (start - em->start)); > + free_extent_map(em); > + em = NULL; > + > + ret = can_nocow_extent(inode, start, &len, NULL, NULL, NULL); > + if (ret < 0) { > + goto out; > + } else if (ret) { > + ret = 0; > + } else { > + btrfs_err(fs_info, "swapfile is copy-on-write"); > + ret = -EINVAL; > + goto out; > + } > + > + em = btrfs_get_chunk_map(fs_info, logical_block_start, len); > + if (IS_ERR(em)) { > + ret = PTR_ERR(em); > + goto out; > + } > + > + if (em->map_lookup->type & BTRFS_BLOCK_GROUP_PROFILE_MASK) { > + btrfs_err(fs_info, "swapfile data profile is not single"); > + ret = -EINVAL; > + goto out; > + } > + > + if (device == NULL) { > + device = em->map_lookup->stripes[0].dev; > + } else if (device != em->map_lookup->stripes[0].dev) { > + btrfs_err(fs_info, "swapfile is on multiple devices"); > + ret = -EINVAL; > + goto out; > + } > + > + physical_block_start = (em->map_lookup->stripes[0].physical + > + (logical_block_start - em->start)); > + len = min(len, em->len - (logical_block_start - em->start)); > + free_extent_map(em); > + em = NULL; > + > + if (bsi.block_len && > + bsi.block_start + bsi.block_len == physical_block_start) { > + bsi.block_len += len; > + } else { > + if (bsi.block_len) { > + ret = btrfs_add_swap_extent(sis, &bsi); > + if (ret) > + goto out; > + } > + bsi.start = start; > + bsi.block_start = physical_block_start; > + bsi.block_len = len; > + } > + > + start = end; > + } > + > + if (bsi.block_len) > + ret = btrfs_add_swap_extent(sis, &bsi); > + > +out: > + if (!IS_ERR_OR_NULL(em)) > + free_extent_map(em); > + > + unlock_extent_cached(io_tree, 0, isize - 1, &cached_state); > + > + clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags); > + > + if (ret) { > + atomic_dec(&BTRFS_I(inode)->root->nr_swapfiles); > + atomic_dec(&fs_info->nr_swapfiles); > + return ret; > + } Clearing the EXCL_OP should be done here, so the order of release is reversed so the contexts are properly nested. > + > + if (device) > + sis->bdev = device->bdev; > + *span = bsi.highest_ppage - bsi.lowest_ppage + 1; > + sis->max = bsi.nr_pages; > + sis->pages = bsi.nr_pages - 1; > + sis->highest_bit = bsi.nr_pages - 1; > + return bsi.nr_extents; > +} > + > +static void btrfs_swap_deactivate(struct file *file) > +{ > + struct inode *inode = file_inode(file); > + > + atomic_dec(&BTRFS_I(inode)->root->nr_swapfiles); > + atomic_dec(&BTRFS_I(inode)->root->fs_info->nr_swapfiles); > +} > + > static const struct inode_operations btrfs_dir_inode_operations = { > .getattr = btrfs_getattr, > .lookup = btrfs_lookup, > @@ -10606,6 +10824,8 @@ static const struct address_space_operations btrfs_aops = { > .releasepage = btrfs_releasepage, > .set_page_dirty = btrfs_set_page_dirty, > .error_remove_page = generic_error_remove_page, > + .swap_activate = btrfs_swap_activate, > + .swap_deactivate = btrfs_swap_deactivate, > }; > > static const struct address_space_operations btrfs_symlink_aops = { > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 886c9d89b144..0d934b5be05c 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -2382,6 +2382,7 @@ add_swap_extent(struct swap_info_struct *sis, unsigned long start_page, > list_add_tail(&new_se->list, &sis->first_swap_extent.list); > return 1; > } > +EXPORT_SYMBOL_GPL(add_swap_extent); This maybe needs to go as a separate patch as it's an export in a different subsystem, unless ou get an ack to do it in the same patch.