Alex Shi <alex.shi@xxxxxxxxxx> writes:
> Hi Dmitry&Theodore,
>
> Someone said without the following patch on lts 3.10 kernel (which used
> as android base kernel). the write maybe very very slow, needs 1 or 2
> seconds to finish.
In fact this was an optimization.
wait_for_stable_page() is actually and optimized wait_on_page_writeback()
see:
void wait_for_stable_page(struct page *page)
{
struct address_space *mapping = page_mapping(page);
struct backing_dev_info *bdi =
mapping->backing_dev_info;
if (!bdi_cap_stable_pages_required(bdi))
return;
wait_on_page_writeback(page);
}
It is very unlikely the patch provokes such huge slowdown.
Can you please repeat your measurements and double check your evidence.
>
> I quick looked this patch, seems it's no harm for a normal fs function.
> but still don't know why it is helpful. So do you remember why you
> commit this change at that time?
>
> Thanks
> Alex
>
> ommit 7afe5aa59ed3da7b6161617e7f157c7c680dc41e
> Author: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
> Date: Wed Aug 28 14:30:47 2013 -0400
>
> ext4: convert write_begin methods to stable_page_writes semantics
>
> Use wait_for_stable_page() instead of wait_on_page_writeback()
>
> Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
> Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
> Reviewed-by: Jan Kara <jack@xxxxxxx>
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index fc4051e..47c8e46 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -969,7 +969,8 @@ retry_journal:
> ext4_journal_stop(handle);
> goto retry_grab;
> }
> - wait_on_page_writeback(page);
> + /* In case writeback began while the page was unlocked */
> + wait_for_stable_page(page);
>
> if (ext4_should_dioread_nolock(inode))
> ret = __block_write_begin(page, pos, len,
> ext4_get_block_write);
> @@ -2678,7 +2679,7 @@ retry_journal:
> goto retry_grab;
> }
> /* In case writeback began while the page was unlocked */
> - wait_on_page_writeback(page);
> + wait_for_stable_page(page);
>
> ret = __block_write_begin(page, pos, len, ext4_da_get_block_prep);
> if (ret < 0) {
> ~
>
> --
> Thanks
> Alex
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