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    SubjectRe: [PATCH 01/17] writeback: introduce wbc.tagged_sync for the WB_SYNC_NONE sync stage
    On Fri 06-05-11 11:08:22, Wu Fengguang wrote:
    > sync(2) is performed in two stages: the WB_SYNC_NONE sync and the
    > WB_SYNC_ALL sync. Tag the first stage with wbc.tagged_sync and do
    > livelock prevention for it, too.
    >
    > Note that writeback_inodes_sb() is called by not only sync(), they are
    > treated the same because the other callers also need livelock prevention.
    >
    > Impact: It changes the order in which pages/inodes are synced to disk.
    > Now in the WB_SYNC_NONE stage, it won't proceed to write the next inode
    > until finished with the current inode.
    You can add:
    Acked-by: Jan Kara <jack@suse.cz>

    > CC: Jan Kara <jack@suse.cz>
    > CC: Dave Chinner <david@fromorbit.com>
    > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    > ---
    > fs/ext4/inode.c | 4 ++--
    > fs/fs-writeback.c | 9 +++++----
    > include/linux/writeback.h | 1 +
    > mm/page-writeback.c | 4 ++--
    > 4 files changed, 10 insertions(+), 8 deletions(-)
    >
    > --- linux-next.orig/fs/fs-writeback.c 2011-05-05 23:29:51.000000000 +0800
    > +++ linux-next/fs/fs-writeback.c 2011-05-05 23:30:22.000000000 +0800
    > @@ -36,6 +36,7 @@ struct wb_writeback_work {
    > long nr_pages;
    > struct super_block *sb;
    > enum writeback_sync_modes sync_mode;
    > + unsigned int tagged_sync:1;
    > unsigned int for_kupdate:1;
    > unsigned int range_cyclic:1;
    > unsigned int for_background:1;
    > @@ -650,6 +651,7 @@ static long wb_writeback(struct bdi_writ
    > {
    > struct writeback_control wbc = {
    > .sync_mode = work->sync_mode,
    > + .tagged_sync = work->tagged_sync,
    > .older_than_this = NULL,
    > .for_kupdate = work->for_kupdate,
    > .for_background = work->for_background,
    > @@ -657,7 +659,7 @@ static long wb_writeback(struct bdi_writ
    > };
    > unsigned long oldest_jif;
    > long wrote = 0;
    > - long write_chunk;
    > + long write_chunk = MAX_WRITEBACK_PAGES;
    > struct inode *inode;
    >
    > if (wbc.for_kupdate) {
    > @@ -683,9 +685,7 @@ static long wb_writeback(struct bdi_writ
    > * (quickly) tag currently dirty pages
    > * (maybe slowly) sync all tagged pages
    > */
    > - if (wbc.sync_mode == WB_SYNC_NONE)
    > - write_chunk = MAX_WRITEBACK_PAGES;
    > - else
    > + if (wbc.sync_mode == WB_SYNC_ALL || wbc.tagged_sync)
    > write_chunk = LONG_MAX;
    >
    > wbc.wb_start = jiffies; /* livelock avoidance */
    > @@ -1193,6 +1193,7 @@ void writeback_inodes_sb_nr(struct super
    > struct wb_writeback_work work = {
    > .sb = sb,
    > .sync_mode = WB_SYNC_NONE,
    > + .tagged_sync = 1,
    > .done = &done,
    > .nr_pages = nr,
    > };
    > --- linux-next.orig/include/linux/writeback.h 2011-05-05 23:29:51.000000000 +0800
    > +++ linux-next/include/linux/writeback.h 2011-05-05 23:30:22.000000000 +0800
    > @@ -47,6 +47,7 @@ struct writeback_control {
    > unsigned encountered_congestion:1; /* An output: a queue is full */
    > unsigned for_kupdate:1; /* A kupdate writeback */
    > unsigned for_background:1; /* A background writeback */
    > + unsigned tagged_sync:1; /* do livelock prevention for sync */
    > unsigned for_reclaim:1; /* Invoked from the page allocator */
    > unsigned range_cyclic:1; /* range_start is cyclic */
    > unsigned more_io:1; /* more io to be dispatched */
    > --- linux-next.orig/mm/page-writeback.c 2011-05-05 23:29:51.000000000 +0800
    > +++ linux-next/mm/page-writeback.c 2011-05-05 23:30:22.000000000 +0800
    > @@ -892,12 +892,12 @@ int write_cache_pages(struct address_spa
    > range_whole = 1;
    > cycled = 1; /* ignore range_cyclic tests */
    > }
    > - if (wbc->sync_mode == WB_SYNC_ALL)
    > + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_sync)
    > tag = PAGECACHE_TAG_TOWRITE;
    > else
    > tag = PAGECACHE_TAG_DIRTY;
    > retry:
    > - if (wbc->sync_mode == WB_SYNC_ALL)
    > + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_sync)
    > tag_pages_for_writeback(mapping, index, end);
    > done_index = index;
    > while (!done && (index <= end)) {
    > --- linux-next.orig/fs/ext4/inode.c 2011-05-05 23:29:51.000000000 +0800
    > +++ linux-next/fs/ext4/inode.c 2011-05-05 23:30:22.000000000 +0800
    > @@ -2741,7 +2741,7 @@ static int write_cache_pages_da(struct a
    > index = wbc->range_start >> PAGE_CACHE_SHIFT;
    > end = wbc->range_end >> PAGE_CACHE_SHIFT;
    >
    > - if (wbc->sync_mode == WB_SYNC_ALL)
    > + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_sync)
    > tag = PAGECACHE_TAG_TOWRITE;
    > else
    > tag = PAGECACHE_TAG_DIRTY;
    > @@ -2975,7 +2975,7 @@ static int ext4_da_writepages(struct add
    > }
    >
    > retry:
    > - if (wbc->sync_mode == WB_SYNC_ALL)
    > + if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_sync)
    > tag_pages_for_writeback(mapping, index, end);
    >
    > while (!ret && wbc->nr_to_write > 0) {
    >
    >
    --
    Jan Kara <jack@suse.cz>
    SUSE Labs, CR


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