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Date: Wed, 8 May 2013 14:57:13 +0800
From: Zheng Liu <gnehzuil.liu@...il.com>
To: Jan Kara <jack@...e.cz>
Cc: Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 20/29] ext4: Use transaction reservation for extent
conversion in ext4_end_io
On Mon, Apr 08, 2013 at 11:32:25PM +0200, Jan Kara wrote:
> Later we would like to clear PageWriteback bit only after extent conversion
> from unwritten to written extents is performed. However it is not possible
> to start a transaction after PageWriteback is set because that violates
> lock ordering (and is easy to deadlock). So we have to reserve a transaction
> before locking pages and sending them for IO and later we use the transaction
> for extent conversion from ext4_end_io().
>
> Signed-off-by: Jan Kara <jack@...e.cz>
Reviewed-by: Zheng Liu <wenqing.lz@...bao.com>
Regards,
- Zheng
> ---
> fs/ext4/ext4.h | 12 +++++++++---
> fs/ext4/ext4_jbd2.h | 3 ++-
> fs/ext4/extents.c | 39 ++++++++++++++++++++++++++++-----------
> fs/ext4/inode.c | 32 ++++++++++++++++++++++++++++++--
> fs/ext4/page-io.c | 11 ++++++++---
> 5 files changed, 77 insertions(+), 20 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 3c3827a..65adf0d 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -182,10 +182,13 @@ struct ext4_map_blocks {
> #define EXT4_IO_END_DIRECT 0x0004
>
> /*
> - * For converting uninitialized extents on a work queue.
> + * For converting uninitialized extents on a work queue. 'handle' is used for
> + * buffered writeback.
> */
> typedef struct ext4_io_end {
> struct list_head list; /* per-file finished IO list */
> + handle_t *handle; /* handle reserved for extent
> + * conversion */
> struct inode *inode; /* file being written to */
> unsigned int flag; /* unwritten or not */
> loff_t offset; /* offset in the file */
> @@ -1314,6 +1317,9 @@ static inline void ext4_set_io_unwritten_flag(struct inode *inode,
> struct ext4_io_end *io_end)
> {
> if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
> + /* Writeback has to have coversion transaction reserved */
> + WARN_ON(!io_end->handle &&
> + !(io_end->flag & EXT4_IO_END_DIRECT));
> io_end->flag |= EXT4_IO_END_UNWRITTEN;
> atomic_inc(&EXT4_I(inode)->i_unwritten);
> }
> @@ -2550,8 +2556,8 @@ extern void ext4_ext_init(struct super_block *);
> extern void ext4_ext_release(struct super_block *);
> extern long ext4_fallocate(struct file *file, int mode, loff_t offset,
> loff_t len);
> -extern int ext4_convert_unwritten_extents(struct inode *inode, loff_t offset,
> - ssize_t len);
> +extern int ext4_convert_unwritten_extents(handle_t *handle, struct inode *inode,
> + loff_t offset, ssize_t len);
> extern int ext4_map_blocks(handle_t *handle, struct inode *inode,
> struct ext4_map_blocks *map, int flags);
> extern int ext4_ext_calc_metadata_amount(struct inode *inode,
> diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
> index bb17931..88e95d7 100644
> --- a/fs/ext4/ext4_jbd2.h
> +++ b/fs/ext4/ext4_jbd2.h
> @@ -132,7 +132,8 @@ static inline int ext4_jbd2_credits_xattr(struct inode *inode)
> #define EXT4_HT_MIGRATE 8
> #define EXT4_HT_MOVE_EXTENTS 9
> #define EXT4_HT_XATTR 10
> -#define EXT4_HT_MAX 11
> +#define EXT4_HT_EXT_CONVERT 11
> +#define EXT4_HT_MAX 12
>
> /**
> * struct ext4_journal_cb_entry - Base structure for callback information.
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 8064b71..ae22735 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -4484,10 +4484,9 @@ retry:
> * function, to convert the fallocated extents after IO is completed.
> * Returns 0 on success.
> */
> -int ext4_convert_unwritten_extents(struct inode *inode, loff_t offset,
> - ssize_t len)
> +int ext4_convert_unwritten_extents(handle_t *handle, struct inode *inode,
> + loff_t offset, ssize_t len)
> {
> - handle_t *handle;
> unsigned int max_blocks;
> int ret = 0;
> int ret2 = 0;
> @@ -4502,16 +4501,31 @@ int ext4_convert_unwritten_extents(struct inode *inode, loff_t offset,
> max_blocks = ((EXT4_BLOCK_ALIGN(len + offset, blkbits) >> blkbits) -
> map.m_lblk);
> /*
> - * credits to insert 1 extent into extent tree
> + * This is somewhat ugly but the idea is clear: When transaction is
> + * reserved, everything goes into it. Otherwise we rather start several
> + * smaller transactions for conversion of each extent separately.
> */
> - credits = ext4_chunk_trans_blocks(inode, max_blocks);
> + if (handle) {
> + handle = ext4_journal_start_reserved(handle);
> + if (IS_ERR(handle))
> + return PTR_ERR(handle);
> + credits = 0;
> + } else {
> + /*
> + * credits to insert 1 extent into extent tree
> + */
> + credits = ext4_chunk_trans_blocks(inode, max_blocks);
> + }
> while (ret >= 0 && ret < max_blocks) {
> map.m_lblk += ret;
> map.m_len = (max_blocks -= ret);
> - handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS, credits);
> - if (IS_ERR(handle)) {
> - ret = PTR_ERR(handle);
> - break;
> + if (credits) {
> + handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS,
> + credits);
> + if (IS_ERR(handle)) {
> + ret = PTR_ERR(handle);
> + break;
> + }
> }
> ret = ext4_map_blocks(handle, inode, &map,
> EXT4_GET_BLOCKS_IO_CONVERT_EXT);
> @@ -4522,10 +4536,13 @@ int ext4_convert_unwritten_extents(struct inode *inode, loff_t offset,
> inode->i_ino, map.m_lblk,
> map.m_len, ret);
> ext4_mark_inode_dirty(handle, inode);
> - ret2 = ext4_journal_stop(handle);
> - if (ret <= 0 || ret2 )
> + if (credits)
> + ret2 = ext4_journal_stop(handle);
> + if (ret <= 0 || ret2)
> break;
> }
> + if (!credits)
> + ret2 = ext4_journal_stop(handle);
> return ret > 0 ? ret2 : ret;
> }
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 0602a09..f8e78ce 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -1327,6 +1327,8 @@ static void ext4_da_page_release_reservation(struct page *page,
> struct mpage_da_data {
> struct inode *inode;
> struct writeback_control *wbc;
> + handle_t *reserved_handle; /* Handle reserved for conversion */
> +
> pgoff_t first_page; /* The first page to write */
> pgoff_t next_page; /* Current page to examine */
> pgoff_t last_page; /* Last page to examine */
> @@ -1973,8 +1975,13 @@ static int mpage_map_one_extent(handle_t *handle, struct mpage_da_data *mpd)
> err = ext4_map_blocks(handle, inode, map, get_blocks_flags);
> if (err < 0)
> return err;
> - if (map->m_flags & EXT4_MAP_UNINIT)
> + if (map->m_flags & EXT4_MAP_UNINIT) {
> + if (!mpd->io_submit.io_end->handle) {
> + mpd->io_submit.io_end->handle = mpd->reserved_handle;
> + mpd->reserved_handle = NULL;
> + }
> ext4_set_io_unwritten_flag(inode, mpd->io_submit.io_end);
> + }
>
> BUG_ON(map->m_len == 0);
> if (map->m_flags & EXT4_MAP_NEW) {
> @@ -2274,6 +2281,7 @@ static int ext4_da_writepages(struct address_space *mapping,
>
> mpd.inode = inode;
> mpd.wbc = wbc;
> + mpd.reserved_handle = NULL;
> ext4_io_submit_init(&mpd.io_submit, wbc);
> retry:
> if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
> @@ -2288,6 +2296,23 @@ retry:
> break;
> }
>
> + /* Reserve handle if it may be needed for extent conversion */
> + if (ext4_should_dioread_nolock(inode) && !mpd.reserved_handle) {
> + /*
> + * We may need to convert upto one extent per block in
> + * the page and we may dirty the inode.
> + */
> + mpd.reserved_handle = ext4_journal_reserve(inode,
> + EXT4_HT_EXT_CONVERT,
> + 1 + (PAGE_CACHE_SIZE >> inode->i_blkbits));
> + if (IS_ERR(mpd.reserved_handle)) {
> + ret = PTR_ERR(mpd.reserved_handle);
> + mpd.reserved_handle = NULL;
> + ext4_put_io_end(mpd.io_submit.io_end);
> + break;
> + }
> + }
> +
> /*
> * We have two constraints: We find one extent to map and we
> * must always write out whole page (makes a difference when
> @@ -2364,6 +2389,9 @@ retry:
> */
> mapping->writeback_index = mpd.first_page;
>
> + if (mpd.reserved_handle)
> + ext4_journal_free_reserved(mpd.reserved_handle);
> +
> out_writepages:
> trace_ext4_da_writepages_result(inode, wbc, ret,
> nr_to_write - wbc->nr_to_write);
> @@ -2977,7 +3005,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
> * for non AIO case, since the IO is already
> * completed, we could do the conversion right here
> */
> - err = ext4_convert_unwritten_extents(inode,
> + err = ext4_convert_unwritten_extents(NULL, inode,
> offset, ret);
> if (err < 0)
> ret = err;
> diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
> index cc59cd9..e8ee4da 100644
> --- a/fs/ext4/page-io.c
> +++ b/fs/ext4/page-io.c
> @@ -55,6 +55,7 @@ static void ext4_release_io_end(ext4_io_end_t *io_end)
> {
> BUG_ON(!list_empty(&io_end->list));
> BUG_ON(io_end->flag & EXT4_IO_END_UNWRITTEN);
> + WARN_ON(io_end->handle);
>
> if (atomic_dec_and_test(&EXT4_I(io_end->inode)->i_ioend_count))
> wake_up_all(ext4_ioend_wq(io_end->inode));
> @@ -81,13 +82,15 @@ static int ext4_end_io(ext4_io_end_t *io)
> struct inode *inode = io->inode;
> loff_t offset = io->offset;
> ssize_t size = io->size;
> + handle_t *handle = io->handle;
> int ret = 0;
>
> ext4_debug("ext4_end_io_nolock: io 0x%p from inode %lu,list->next 0x%p,"
> "list->prev 0x%p\n",
> io, inode->i_ino, io->list.next, io->list.prev);
>
> - ret = ext4_convert_unwritten_extents(inode, offset, size);
> + io->handle = NULL; /* Following call will use up the handle */
> + ret = ext4_convert_unwritten_extents(handle, inode, offset, size);
> if (ret < 0) {
> ext4_msg(inode->i_sb, KERN_EMERG,
> "failed to convert unwritten extents to written "
> @@ -217,8 +220,10 @@ int ext4_put_io_end(ext4_io_end_t *io_end)
>
> if (atomic_dec_and_test(&io_end->count)) {
> if (io_end->flag & EXT4_IO_END_UNWRITTEN) {
> - err = ext4_convert_unwritten_extents(io_end->inode,
> - io_end->offset, io_end->size);
> + err = ext4_convert_unwritten_extents(io_end->handle,
> + io_end->inode, io_end->offset,
> + io_end->size);
> + io_end->handle = NULL;
> ext4_clear_io_unwritten_flag(io_end);
> }
> ext4_release_io_end(io_end);
> --
> 1.7.1
>
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