On Fri, 20 Apr 2007 17:52:02 +0200 Peter Zijlstra <[email protected]> wrote:
> Count per BDI writeback pages.
>
> Signed-off-by: Peter Zijlstra <[email protected]>
> ---
> include/linux/backing-dev.h | 1 +
> mm/page-writeback.c | 12 ++++++++++--
> 2 files changed, 11 insertions(+), 2 deletions(-)
>
> Index: linux-2.6/mm/page-writeback.c
> ===================================================================
> --- linux-2.6.orig/mm/page-writeback.c 2007-04-20 15:27:28.000000000 +0200
> +++ linux-2.6/mm/page-writeback.c 2007-04-20 15:28:10.000000000 +0200
> @@ -979,14 +979,18 @@ int test_clear_page_writeback(struct pag
> int ret;
>
> if (mapping) {
> + struct backing_dev_info *bdi = mapping->backing_dev_info;
> unsigned long flags;
>
> write_lock_irqsave(&mapping->tree_lock, flags);
> ret = TestClearPageWriteback(page);
> - if (ret)
> + if (ret) {
> radix_tree_tag_clear(&mapping->page_tree,
> page_index(page),
> PAGECACHE_TAG_WRITEBACK);
> + if (bdi_cap_writeback_dirty(bdi))
> + __dec_bdi_stat(bdi, BDI_WRITEBACK);
Why do we test bdi_cap_writeback_dirty() here?
If we remove that test, we end up accumulating statistics for
non-writebackable backing devs, but does that matter? Probably the common
case is writebackable backing-devs, so eliminating the test-n-branch might
be a net microgain.
-
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