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Date: Wed, 16 Sep 2009 15:36:31 +0200
From: Jan Kara <jack@...e.cz>
To: Jens Axboe <jens.axboe@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
chris.mason@...cle.com, hch@...radead.org, tytso@....edu,
akpm@...ux-foundation.org, jack@...e.cz, trond.myklebust@....uio.no
Subject: Re: [PATCH 09/16] writeback: separate starting of sync vs
opportunistic writeback
On Wed 16-09-09 15:24:47, Jens Axboe wrote:
> bdi_start_writeback() is currently split into two paths, one for
> WB_SYNC_NONE and one for WB_SYNC_ALL. Add bdi_sync_writeback()
> for WB_SYNC_ALL writeback and let bdi_start_writeback() handle
> only WB_SYNC_NONE.
>
> Push down the writeback_control allocation and only accept the
> parameters that make sense for each function. This cleans up
> the API considerably.
>
Looks good.
Acked-by: Jan Kara <jack@...e.cz>
Honza
> Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
> ---
> fs/fs-writeback.c | 132 ++++++++++++++++++++++---------------------
> fs/ubifs/budget.c | 20 +------
> include/linux/backing-dev.h | 2 +-
> include/linux/writeback.h | 4 +-
> mm/page-writeback.c | 12 +---
> 5 files changed, 75 insertions(+), 95 deletions(-)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 59b3ee6..5887328 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -74,14 +74,10 @@ static inline bool bdi_work_on_stack(struct bdi_work *work)
> }
>
> static inline void bdi_work_init(struct bdi_work *work,
> - struct writeback_control *wbc)
> + struct wb_writeback_args *args)
> {
> INIT_RCU_HEAD(&work->rcu_head);
> - work->args.sb = wbc->sb;
> - work->args.nr_pages = wbc->nr_to_write;
> - work->args.sync_mode = wbc->sync_mode;
> - work->args.range_cyclic = wbc->range_cyclic;
> - work->args.for_kupdate = 0;
> + work->args = *args;
> work->state = WS_USED;
> }
>
> @@ -194,7 +190,7 @@ static void bdi_wait_on_work_clear(struct bdi_work *work)
> }
>
> static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
> - struct writeback_control *wbc)
> + struct wb_writeback_args *args)
> {
> struct bdi_work *work;
>
> @@ -204,7 +200,7 @@ static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
> */
> work = kmalloc(sizeof(*work), GFP_ATOMIC);
> if (work) {
> - bdi_work_init(work, wbc);
> + bdi_work_init(work, args);
> bdi_queue_work(bdi, work);
> } else {
> struct bdi_writeback *wb = &bdi->wb;
> @@ -214,24 +210,54 @@ static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
> }
> }
>
> -void bdi_start_writeback(struct writeback_control *wbc)
> +/**
> + * bdi_sync_writeback - start and wait for writeback
> + * @bdi: the backing device to write from
> + * @sb: write inodes from this super_block
> + *
> + * Description:
> + * This does WB_SYNC_ALL data integrity writeback and waits for the
> + * IO to complete. Callers must hold the sb s_umount semaphore for
> + * reading, to avoid having the super disappear before we are done.
> + */
> +static void bdi_sync_writeback(struct backing_dev_info *bdi,
> + struct super_block *sb)
> {
> - /*
> - * WB_SYNC_NONE is opportunistic writeback. If this allocation fails,
> - * bdi_queue_work() will wake up the thread and flush old data. This
> - * should ensure some amount of progress in freeing memory.
> - */
> - if (wbc->sync_mode != WB_SYNC_ALL)
> - bdi_alloc_queue_work(wbc->bdi, wbc);
> - else {
> - struct bdi_work work;
> + struct wb_writeback_args args = {
> + .sb = sb,
> + .sync_mode = WB_SYNC_ALL,
> + .nr_pages = LONG_MAX,
> + .range_cyclic = 0,
> + };
> + struct bdi_work work;
>
> - bdi_work_init(&work, wbc);
> - work.state |= WS_ONSTACK;
> + bdi_work_init(&work, &args);
> + work.state |= WS_ONSTACK;
>
> - bdi_queue_work(wbc->bdi, &work);
> - bdi_wait_on_work_clear(&work);
> - }
> + bdi_queue_work(bdi, &work);
> + bdi_wait_on_work_clear(&work);
> +}
> +
> +/**
> + * bdi_start_writeback - start writeback
> + * @bdi: the backing device to write from
> + * @nr_pages: the number of pages to write
> + *
> + * Description:
> + * This does WB_SYNC_NONE opportunistic writeback. The IO is only
> + * started when this function returns, we make no guarentees on
> + * completion. Caller need not hold sb s_umount semaphore.
> + *
> + */
> +void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages)
> +{
> + struct wb_writeback_args args = {
> + .sync_mode = WB_SYNC_NONE,
> + .nr_pages = nr_pages,
> + .range_cyclic = 1,
> + };
> +
> + bdi_alloc_queue_work(bdi, &args);
> }
>
> /*
> @@ -863,23 +889,25 @@ int bdi_writeback_task(struct bdi_writeback *wb)
> }
>
> /*
> - * Schedule writeback for all backing devices. Can only be used for
> - * WB_SYNC_NONE writeback, WB_SYNC_ALL should use bdi_start_writeback()
> - * and pass in the superblock.
> + * Schedule writeback for all backing devices. This does WB_SYNC_NONE
> + * writeback, for integrity writeback see bdi_sync_writeback().
> */
> -static void bdi_writeback_all(struct writeback_control *wbc)
> +static void bdi_writeback_all(struct super_block *sb, long nr_pages)
> {
> + struct wb_writeback_args args = {
> + .sb = sb,
> + .nr_pages = nr_pages,
> + .sync_mode = WB_SYNC_NONE,
> + };
> struct backing_dev_info *bdi;
>
> - WARN_ON(wbc->sync_mode == WB_SYNC_ALL);
> -
> rcu_read_lock();
>
> list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
> if (!bdi_has_dirty_io(bdi))
> continue;
>
> - bdi_alloc_queue_work(bdi, wbc);
> + bdi_alloc_queue_work(bdi, &args);
> }
>
> rcu_read_unlock();
> @@ -891,17 +919,10 @@ static void bdi_writeback_all(struct writeback_control *wbc)
> */
> void wakeup_flusher_threads(long nr_pages)
> {
> - struct writeback_control wbc = {
> - .sync_mode = WB_SYNC_NONE,
> - .older_than_this = NULL,
> - .range_cyclic = 1,
> - };
> -
> if (nr_pages == 0)
> nr_pages = global_page_state(NR_FILE_DIRTY) +
> global_page_state(NR_UNSTABLE_NFS);
> - wbc.nr_to_write = nr_pages;
> - bdi_writeback_all(&wbc);
> + bdi_writeback_all(NULL, nr_pages);
> }
>
> static noinline void block_dump___mark_inode_dirty(struct inode *inode)
> @@ -1048,7 +1069,7 @@ EXPORT_SYMBOL(__mark_inode_dirty);
> * on the writer throttling path, and we get decent balancing between many
> * throttled threads: we don't want them all piling up on inode_sync_wait.
> */
> -static void wait_sb_inodes(struct writeback_control *wbc)
> +static void wait_sb_inodes(struct super_block *sb)
> {
> struct inode *inode, *old_inode = NULL;
>
> @@ -1056,7 +1077,7 @@ static void wait_sb_inodes(struct writeback_control *wbc)
> * We need to be protected against the filesystem going from
> * r/o to r/w or vice versa.
> */
> - WARN_ON(!rwsem_is_locked(&wbc->sb->s_umount));
> + WARN_ON(!rwsem_is_locked(&sb->s_umount));
>
> spin_lock(&inode_lock);
>
> @@ -1067,7 +1088,7 @@ static void wait_sb_inodes(struct writeback_control *wbc)
> * In which case, the inode may not be on the dirty list, but
> * we still have to wait for that writeout.
> */
> - list_for_each_entry(inode, &wbc->sb->s_inodes, i_sb_list) {
> + list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
> struct address_space *mapping;
>
> if (inode->i_state & (I_FREEING|I_CLEAR|I_WILL_FREE|I_NEW))
> @@ -1107,14 +1128,8 @@ static void wait_sb_inodes(struct writeback_control *wbc)
> * for IO completion of submitted IO. The number of pages submitted is
> * returned.
> */
> -long writeback_inodes_sb(struct super_block *sb)
> +void writeback_inodes_sb(struct super_block *sb)
> {
> - struct writeback_control wbc = {
> - .sb = sb,
> - .sync_mode = WB_SYNC_NONE,
> - .range_start = 0,
> - .range_end = LLONG_MAX,
> - };
> unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
> unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
> long nr_to_write;
> @@ -1122,9 +1137,7 @@ long writeback_inodes_sb(struct super_block *sb)
> nr_to_write = nr_dirty + nr_unstable +
> (inodes_stat.nr_inodes - inodes_stat.nr_unused);
>
> - wbc.nr_to_write = nr_to_write;
> - bdi_writeback_all(&wbc);
> - return nr_to_write - wbc.nr_to_write;
> + bdi_writeback_all(sb, nr_to_write);
> }
> EXPORT_SYMBOL(writeback_inodes_sb);
>
> @@ -1135,21 +1148,10 @@ EXPORT_SYMBOL(writeback_inodes_sb);
> * This function writes and waits on any dirty inode belonging to this
> * super_block. The number of pages synced is returned.
> */
> -long sync_inodes_sb(struct super_block *sb)
> +void sync_inodes_sb(struct super_block *sb)
> {
> - struct writeback_control wbc = {
> - .sb = sb,
> - .bdi = sb->s_bdi,
> - .sync_mode = WB_SYNC_ALL,
> - .range_start = 0,
> - .range_end = LLONG_MAX,
> - };
> - long nr_to_write = LONG_MAX; /* doesn't actually matter */
> -
> - wbc.nr_to_write = nr_to_write;
> - bdi_start_writeback(&wbc);
> - wait_sb_inodes(&wbc);
> - return nr_to_write - wbc.nr_to_write;
> + bdi_sync_writeback(sb->s_bdi, sb);
> + wait_sb_inodes(sb);
> }
> EXPORT_SYMBOL(sync_inodes_sb);
>
> diff --git a/fs/ubifs/budget.c b/fs/ubifs/budget.c
> index 1c8991b..ee1ce68 100644
> --- a/fs/ubifs/budget.c
> +++ b/fs/ubifs/budget.c
> @@ -54,29 +54,15 @@
> * @nr_to_write: how many dirty pages to write-back
> *
> * This function shrinks UBIFS liability by means of writing back some amount
> - * of dirty inodes and their pages. Returns the amount of pages which were
> - * written back. The returned value does not include dirty inodes which were
> - * synchronized.
> + * of dirty inodes and their pages.
> *
> * Note, this function synchronizes even VFS inodes which are locked
> * (@i_mutex) by the caller of the budgeting function, because write-back does
> * not touch @i_mutex.
> */
> -static int shrink_liability(struct ubifs_info *c, int nr_to_write)
> +static void shrink_liability(struct ubifs_info *c, int nr_to_write)
> {
> - int nr_written;
> -
> - nr_written = writeback_inodes_sb(c->vfs_sb);
> - if (!nr_written) {
> - /*
> - * Re-try again but wait on pages/inodes which are being
> - * written-back concurrently (e.g., by pdflush).
> - */
> - nr_written = sync_inodes_sb(c->vfs_sb);
> - }
> -
> - dbg_budg("%d pages were written back", nr_written);
> - return nr_written;
> + writeback_inodes_sb(c->vfs_sb);
> }
>
> /**
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index 859e797..0ee33c2 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -101,7 +101,7 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
> const char *fmt, ...);
> int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
> void bdi_unregister(struct backing_dev_info *bdi);
> -void bdi_start_writeback(struct writeback_control *wbc);
> +void bdi_start_writeback(struct backing_dev_info *bdi, long nr_pages);
> int bdi_writeback_task(struct bdi_writeback *wb);
> int bdi_has_dirty_io(struct backing_dev_info *bdi);
>
> diff --git a/include/linux/writeback.h b/include/linux/writeback.h
> index 48a054e..75cf586 100644
> --- a/include/linux/writeback.h
> +++ b/include/linux/writeback.h
> @@ -68,8 +68,8 @@ struct writeback_control {
> */
> struct bdi_writeback;
> int inode_wait(void *);
> -long writeback_inodes_sb(struct super_block *);
> -long sync_inodes_sb(struct super_block *);
> +void writeback_inodes_sb(struct super_block *);
> +void sync_inodes_sb(struct super_block *);
> void writeback_inodes_wbc(struct writeback_control *wbc);
> long wb_do_writeback(struct bdi_writeback *wb, int force_wait);
> void wakeup_flusher_threads(long nr_pages);
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 12c3d84..1eea4fa 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -582,16 +582,8 @@ static void balance_dirty_pages(struct address_space *mapping)
> if ((laptop_mode && pages_written) ||
> (!laptop_mode && ((nr_writeback = global_page_state(NR_FILE_DIRTY)
> + global_page_state(NR_UNSTABLE_NFS))
> - > background_thresh))) {
> - struct writeback_control wbc = {
> - .bdi = bdi,
> - .sync_mode = WB_SYNC_NONE,
> - .nr_to_write = nr_writeback,
> - };
> -
> -
> - bdi_start_writeback(&wbc);
> - }
> + > background_thresh)))
> + bdi_start_writeback(bdi, nr_writeback);
> }
>
> void set_page_dirty_balance(struct page *page, int page_mkwrite)
> --
> 1.6.4.1.207.g68ea
>
--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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