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    SubjectRe: [PATCH 10/17] writeback: avoid extra sync work at enqueue time
    On Fri 06-05-11 11:08:31, Wu Fengguang wrote:
    > This removes writeback_control.wb_start and does more straightforward
    > sync livelock prevention by setting .older_than_this to prevent extra
    > inodes from being enqueued in the first place.
    >
    > CC: Jan Kara <jack@suse.cz>
    Acked-by: Jan Kara <jack@suse.cz>

    Honza

    > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    > ---
    > fs/fs-writeback.c | 16 +++-------------
    > include/linux/writeback.h | 3 ---
    > 2 files changed, 3 insertions(+), 16 deletions(-)
    >
    > --- linux-next.orig/fs/fs-writeback.c 2011-05-05 23:30:29.000000000 +0800
    > +++ linux-next/fs/fs-writeback.c 2011-05-05 23:30:30.000000000 +0800
    > @@ -544,15 +544,6 @@ static int writeback_sb_inodes(struct su
    > continue;
    > }
    >
    > - /*
    > - * Was this inode dirtied after sync_sb_inodes was called?
    > - * This keeps sync from extra jobs and livelock.
    > - */
    > - if (inode_dirtied_after(inode, wbc->wb_start)) {
    > - spin_unlock(&inode->i_lock);
    > - return 1;
    > - }
    > -
    > __iget(inode);
    >
    > pages_skipped = wbc->pages_skipped;
    > @@ -585,9 +576,6 @@ static void __writeback_inodes_wb(struct
    > {
    > int ret = 0;
    >
    > - if (!wbc->wb_start)
    > - wbc->wb_start = jiffies; /* livelock avoidance */
    > -
    > while (!list_empty(&wb->b_io)) {
    > struct inode *inode = wb_inode(wb->b_io.prev);
    > struct super_block *sb = inode->i_sb;
    > @@ -686,7 +674,9 @@ static long wb_writeback(struct bdi_writ
    > if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_sync)
    > write_chunk = LONG_MAX;
    >
    > - wbc.wb_start = jiffies; /* livelock avoidance */
    > + oldest_jif = jiffies;
    > + wbc.older_than_this = &oldest_jif;
    > +
    > for (;;) {
    > /*
    > * Stop writeback when nr_pages has been consumed
    > --- linux-next.orig/include/linux/writeback.h 2011-05-05 23:30:28.000000000 +0800
    > +++ linux-next/include/linux/writeback.h 2011-05-05 23:30:30.000000000 +0800
    > @@ -26,9 +26,6 @@ struct writeback_control {
    > enum writeback_sync_modes sync_mode;
    > unsigned long *older_than_this; /* If !NULL, only write back inodes
    > older than this */
    > - unsigned long wb_start; /* Time writeback_inodes_wb was
    > - called. This is needed to avoid
    > - extra jobs and livelock */
    > long nr_to_write; /* Write this many pages, and decrement
    > this for each page written */
    > long pages_skipped; /* Pages which were not written */
    >
    >
    --
    Jan Kara <jack@suse.cz>
    SUSE Labs, CR


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