On Wed 26-12-12 01:22:36, Sha Zhengju wrote:
> From: Sha Zhengju <handai.szj@xxxxxxxxxx>
>
> Commit a8e7d49a(Fix race in create_empty_buffers() vs __set_page_dirty_buffers())
> extracts TestSetPageDirty from __set_page_dirty and is far away from
> account_page_dirtied. But it's better to make the two operations in one single
> function to keep modular. So in order to avoid the potential race mentioned in
> commit a8e7d49a, we can hold private_lock until __set_page_dirty completes.
> There's no deadlock between ->private_lock and ->tree_lock after confirmation.
Could you be more specific here? E.g. quote mm/filemap.c comment I have
mentioned during the first round of review?
> It's a prepare patch for following memcg dirty page accounting patches.
>
>
> Here is some test numbers that before/after this patch:
> Test steps(Mem-4g, ext4):
> drop_cache; sync
> fio (ioengine=sync/write/buffered/bs=4k/size=1g/numjobs=2/group_reporting/thread)
Could also add some rationale why you think this test is relevant?
> We test it for 10 times and get the average numbers:
> Before:
> write: io=2048.0MB, bw=254117KB/s, iops=63528.9 , runt= 8279msec
> lat (usec): min=1 , max=742361 , avg=30.918, stdev=1601.02
> After:
> write: io=2048.0MB, bw=254044KB/s, iops=63510.3 , runt= 8274.4msec
> lat (usec): min=1 , max=856333 , avg=31.043, stdev=1769.32
>
> Note that the impact is little(<1%).
>
>
> Signed-off-by: Sha Zhengju <handai.szj@xxxxxxxxxx>
> Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
> ---
> fs/buffer.c | 24 ++++++++++++------------
> 1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index c017a2d..3b032b9 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -609,9 +609,15 @@ EXPORT_SYMBOL(mark_buffer_dirty_inode);
> * If warn is true, then emit a warning if the page is not uptodate and has
> * not been truncated.
> */
> -static void __set_page_dirty(struct page *page,
> +static int __set_page_dirty(struct page *page,
> struct address_space *mapping, int warn)
> {
> + if (unlikely(!mapping))
> + return !TestSetPageDirty(page);
> +
> + if (TestSetPageDirty(page))
> + return 0;
> +
> spin_lock_irq(&mapping->tree_lock);
> if (page->mapping) { /* Race with truncate? */
> WARN_ON_ONCE(warn && !PageUptodate(page));
> @@ -621,6 +627,8 @@ static void __set_page_dirty(struct page *page,
> }
> spin_unlock_irq(&mapping->tree_lock);
> __mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> +
> + return 1;
> }
>
> /*
> @@ -666,11 +674,9 @@ int __set_page_dirty_buffers(struct page *page)
> bh = bh->b_this_page;
> } while (bh != head);
> }
> - newly_dirty = !TestSetPageDirty(page);
> + newly_dirty = __set_page_dirty(page, mapping, 1);
> spin_unlock(&mapping->private_lock);
>
> - if (newly_dirty)
> - __set_page_dirty(page, mapping, 1);
> return newly_dirty;
> }
> EXPORT_SYMBOL(__set_page_dirty_buffers);
> @@ -1125,14 +1131,8 @@ void mark_buffer_dirty(struct buffer_head *bh)
> return;
> }
>
> - if (!test_set_buffer_dirty(bh)) {
> - struct page *page = bh->b_page;
> - if (!TestSetPageDirty(page)) {
> - struct address_space *mapping = page_mapping(page);
> - if (mapping)
> - __set_page_dirty(page, mapping, 0);
> - }
> - }
> + if (!test_set_buffer_dirty(bh))
> + __set_page_dirty(bh->b_page, page_mapping(bh->b_page), 0);
> }
> EXPORT_SYMBOL(mark_buffer_dirty);
>
> --
> 1.7.9.5
>
--
Michal Hocko
SUSE Labs
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