Re: a old issue of ext4 on lts 3.10

Alex Shi alex.shi@linaro.org 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@openvz.org 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@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

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