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    Subject[patch] use pdflush for unused inode writeback
    This is pdflush's first application!  The writeback of
    the unused inodes list by keventd is removed, and a
    pdflush thread is dispatched instead.

    There is a need for exclusion - to prevent all the
    pdflush threads from working against the same request
    queue. This is implemented locally. And this is a
    problem, because other pdflush threads can be dispatched
    to writeback other filesystem objects, and they don't
    know that there's already a pdflush thread working that
    request queue.

    So moving the exclusion into the request queue itself
    is on my things-to-do-list. But the code as-is works
    OK - under a `dbench 100' load the number of pdflush
    instances can grow as high as four or five. Some fine
    tuning is needed...

    Patch is against 2.5.8-pre3+ratcache+readahead+pageprivate+pdflush


    --- 2.5.8-pre3/fs/inode.c~dallocbase-45-pdflush_inodes Tue Apr 9 22:53:11 2002
    +++ 2.5.8-pre3-akpm/fs/inode.c Tue Apr 9 22:53:11 2002
    @@ -433,7 +433,7 @@ void sync_inodes(void)
    }
    }

    -static void try_to_sync_unused_inodes(void * arg)
    +static void try_to_sync_unused_inodes(unsigned long pexclusive)
    {
    struct super_block * sb;
    int nr_inodes = inodes_stat.nr_unused;
    @@ -450,10 +450,9 @@ static void try_to_sync_unused_inodes(vo
    }
    spin_unlock(&sb_lock);
    spin_unlock(&inode_lock);
    + clear_bit(0, (unsigned long *)pexclusive);
    }

    -static struct tq_struct unused_inodes_flush_task;
    -
    /**
    * write_inode_now - write an inode to disk
    * @inode: inode to write to disk
    @@ -746,8 +745,15 @@ void prune_icache(int goal)
    * from here or we're either synchronously dogslow
    * or we deadlock with oom.
    */
    - if (goal)
    - schedule_task(&unused_inodes_flush_task);
    + if (goal) {
    + static unsigned long exclusive;
    +
    + if (!test_and_set_bit(0, &exclusive)) {
    + if (pdflush_operation(try_to_sync_unused_inodes,
    + (unsigned long)&exclusive))
    + clear_bit(0, &exclusive);
    + }
    + }
    }
    /*
    * This is called from kswapd when we think we need some
    @@ -1173,8 +1179,6 @@ void __init inode_init(unsigned long mem
    NULL);
    if (!inode_cachep)
    panic("cannot create inode slab cache");
    -
    - unused_inodes_flush_task.routine = try_to_sync_unused_inodes;
    }

    static inline void do_atime_update(struct inode *inode)
    -
    -
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