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Message-ID: <20110723144454.GB5946@localhost>
Date: Sat, 23 Jul 2011 22:44:54 +0800
From: Wu Fengguang <fengguang.wu@...el.com>
To: Stephen Rothwell <sfr@...b.auug.org.au>
Cc: "linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Dave Chinner <dchinner@...hat.com>,
Christoph Hellwig <hch@...radead.org>,
Al Viro <viro@...IV.linux.org.uk>
Subject: Re: linux-next: manual merge of the writeback tree with the vfs
tree
Hi Stephen,
On Mon, Jul 18, 2011 at 03:34:09PM +0800, Stephen Rothwell wrote:
> Hi Wu,
>
> Today's linux-next merge of the writeback tree got a conflict in
> fs/fs-writeback.c between commit dffe5a6c5214 ("superblock: move
> pin_sb_for_writeback() to fs/super.c") from the vfs tree and commits
> f758eeabeb96 ("writeback: split inode_wb_list_lock into
> bdi_writeback.list_lock") and d46db3d58233 ("writeback: make
> writeback_control.nr_to_write straight") from the writeback tree.
>
> I fixed it up (I think - see below) and can carry the fix as necessary.
OK, please. Thank you very much!
Cheers,
Fengguang
> diff --cc fs/fs-writeback.c
> index b8c507c,6d49439..0000000
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@@ -460,6 -480,63 +480,37 @@@ writeback_single_inode(struct inode *in
> return ret;
> }
>
> -/*
> - * For background writeback the caller does not have the sb pinned
> - * before calling writeback. So make sure that we do pin it, so it doesn't
> - * go away while we are writing inodes from it.
> - */
> -static bool pin_sb_for_writeback(struct super_block *sb)
> -{
> - spin_lock(&sb_lock);
> - if (list_empty(&sb->s_instances)) {
> - spin_unlock(&sb_lock);
> - return false;
> - }
> -
> - sb->s_count++;
> - spin_unlock(&sb_lock);
> -
> - if (down_read_trylock(&sb->s_umount)) {
> - if (sb->s_root)
> - return true;
> - up_read(&sb->s_umount);
> - }
> -
> - put_super(sb);
> - return false;
> -}
> -
> + static long writeback_chunk_size(struct backing_dev_info *bdi,
> + struct wb_writeback_work *work)
> + {
> + long pages;
> +
> + /*
> + * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
> + * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
> + * here avoids calling into writeback_inodes_wb() more than once.
> + *
> + * The intended call sequence for WB_SYNC_ALL writeback is:
> + *
> + * wb_writeback()
> + * writeback_sb_inodes() <== called only once
> + * write_cache_pages() <== called once for each inode
> + * (quickly) tag currently dirty pages
> + * (maybe slowly) sync all tagged pages
> + */
> + if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
> + pages = LONG_MAX;
> + else {
> + pages = min(bdi->avg_write_bandwidth / 2,
> + global_dirty_limit / DIRTY_SCOPE);
> + pages = min(pages, work->nr_pages);
> + pages = round_down(pages + MIN_WRITEBACK_PAGES,
> + MIN_WRITEBACK_PAGES);
> + }
> +
> + return pages;
> + }
> +
> /*
> * Write a portion of b_io inodes which belong to @sb.
> *
> @@@ -559,40 -643,41 +617,41 @@@ static long __writeback_inodes_wb(struc
> struct inode *inode = wb_inode(wb->b_io.prev);
> struct super_block *sb = inode->i_sb;
>
> - if (!pin_sb_for_writeback(sb)) {
> + if (!grab_super_passive(sb)) {
> - requeue_io(inode);
> + requeue_io(inode, wb);
> continue;
> }
> - ret = writeback_sb_inodes(sb, wb, wbc, false);
> + wrote += writeback_sb_inodes(sb, wb, work);
> drop_super(sb);
>
> - if (ret)
> - break;
> + /* refer to the same tests at the end of writeback_sb_inodes */
> + if (wrote) {
> + if (time_is_before_jiffies(start_time + HZ / 10UL))
> + break;
> + if (work->nr_pages <= 0)
> + break;
> + }
> }
> - spin_unlock(&inode_wb_list_lock);
> /* Leave any unwritten inodes on b_io */
> + return wrote;
> }
>
> - static void __writeback_inodes_sb(struct super_block *sb,
> - struct bdi_writeback *wb, struct writeback_control *wbc)
> + long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages)
> {
> - WARN_ON(!rwsem_is_locked(&sb->s_umount));
> + struct wb_writeback_work work = {
> + .nr_pages = nr_pages,
> + .sync_mode = WB_SYNC_NONE,
> + .range_cyclic = 1,
> + };
>
> - spin_lock(&inode_wb_list_lock);
> - if (!wbc->for_kupdate || list_empty(&wb->b_io))
> - queue_io(wb, wbc->older_than_this);
> - writeback_sb_inodes(sb, wb, wbc, true);
> - spin_unlock(&inode_wb_list_lock);
> - }
> + spin_lock(&wb->list_lock);
> + if (list_empty(&wb->b_io))
> + queue_io(wb, NULL);
> + __writeback_inodes_wb(wb, &work);
> + spin_unlock(&wb->list_lock);
>
> - /*
> - * The maximum number of pages to writeout in a single bdi flush/kupdate
> - * operation. We do this so we don't hold I_SYNC against an inode for
> - * enormous amounts of time, which would block a userspace task which has
> - * been forced to throttle against that inode. Also, the code reevaluates
> - * the dirty each time it has written this many pages.
> - */
> - #define MAX_WRITEBACK_PAGES 1024
> + return nr_pages - work.nr_pages;
> + }
>
> static inline bool over_bground_thresh(void)
> {
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