From: Nick Piggin Use a bit spin lock in the first buffer of the page to synchronise asynch IO buffer completions, instead of the global page_uptodate_lock, which is showing some scalabilty problems. Signed-off-by: Nick Piggin Signed-off-by: Andrew Morton --- fs/buffer.c | 25 +++++++++++++++++-------- include/linux/buffer_head.h | 3 +++ 2 files changed, 20 insertions(+), 8 deletions(-) diff -puN fs/buffer.c~page_uptodate-locking-scalability fs/buffer.c --- devel/fs/buffer.c~page_uptodate-locking-scalability 2005-06-29 18:15:27.000000000 -0700 +++ devel-akpm/fs/buffer.c 2005-06-29 18:18:11.000000000 -0700 @@ -513,8 +513,8 @@ static void free_more_memory(void) */ static void end_buffer_async_read(struct buffer_head *bh, int uptodate) { - static DEFINE_SPINLOCK(page_uptodate_lock); unsigned long flags; + struct buffer_head *first; struct buffer_head *tmp; struct page *page; int page_uptodate = 1; @@ -536,7 +536,9 @@ static void end_buffer_async_read(struct * two buffer heads end IO at almost the same time and both * decide that the page is now completely done. */ - spin_lock_irqsave(&page_uptodate_lock, flags); + first = page_buffers(page); + local_irq_save(flags); + bit_spin_lock(BH_Uptodate_Lock, &first->b_state); clear_buffer_async_read(bh); unlock_buffer(bh); tmp = bh; @@ -549,7 +551,8 @@ static void end_buffer_async_read(struct } tmp = tmp->b_this_page; } while (tmp != bh); - spin_unlock_irqrestore(&page_uptodate_lock, flags); + bit_spin_unlock(BH_Uptodate_Lock, &first->b_state); + local_irq_restore(flags); /* * If none of the buffers had errors and they are all @@ -561,7 +564,8 @@ static void end_buffer_async_read(struct return; still_busy: - spin_unlock_irqrestore(&page_uptodate_lock, flags); + bit_spin_unlock(BH_Uptodate_Lock, &first->b_state); + local_irq_restore(flags); return; } @@ -572,8 +576,8 @@ still_busy: void end_buffer_async_write(struct buffer_head *bh, int uptodate) { char b[BDEVNAME_SIZE]; - static DEFINE_SPINLOCK(page_uptodate_lock); unsigned long flags; + struct buffer_head *first; struct buffer_head *tmp; struct page *page; @@ -594,7 +598,10 @@ void end_buffer_async_write(struct buffe SetPageError(page); } - spin_lock_irqsave(&page_uptodate_lock, flags); + first = page_buffers(page); + local_irq_save(flags); + bit_spin_lock(BH_Uptodate_Lock, &first->b_state); + clear_buffer_async_write(bh); unlock_buffer(bh); tmp = bh->b_this_page; @@ -605,12 +612,14 @@ void end_buffer_async_write(struct buffe } tmp = tmp->b_this_page; } - spin_unlock_irqrestore(&page_uptodate_lock, flags); + bit_spin_unlock(BH_Uptodate_Lock, &first->b_state); + local_irq_restore(flags); end_page_writeback(page); return; still_busy: - spin_unlock_irqrestore(&page_uptodate_lock, flags); + bit_spin_unlock(BH_Uptodate_Lock, &first->b_state); + local_irq_restore(flags); return; } diff -puN include/linux/buffer_head.h~page_uptodate-locking-scalability include/linux/buffer_head.h --- devel/include/linux/buffer_head.h~page_uptodate-locking-scalability 2005-06-29 18:15:27.000000000 -0700 +++ devel-akpm/include/linux/buffer_head.h 2005-06-29 18:16:07.000000000 -0700 @@ -19,6 +19,9 @@ enum bh_state_bits { BH_Dirty, /* Is dirty */ BH_Lock, /* Is locked */ BH_Req, /* Has been submitted for I/O */ + BH_Uptodate_Lock,/* Used by the first bh in a page, to serialise + * IO completion of other buffers in the page + */ BH_Mapped, /* Has a disk mapping */ BH_New, /* Disk mapping was newly created by get_block */ _