Re: remove iomap_writepage v2

[Jan Kara <jack@suse.cz>]

Hi Christoph!

On Tue 19-07-22 06:13:07, Christoph Hellwig wrote:
> this series removes iomap_writepage and it's callers, following what xfs
> has been doing for a long time.

So this effectively means "no writeback from page reclaim for these
filesystems" AFAICT (page migration of dirty pages seems to be handled by
iomap_migrate_page()) which is going to make life somewhat harder for
memory reclaim when memory pressure is high enough that dirty pages are
reaching end of the LRU list. I don't expect this to be a problem on big
machines but it could have some undesirable effects for small ones
(embedded, small VMs). I agree per-page writeback has been a bad idea for
efficiency reasons for at least last 10-15 years and most filesystems
stopped dealing with more complex situations (like block allocation) from
->writepage() already quite a few years ago without any bug reports AFAIK.
So it all seems like a sensible idea from FS POV but are MM people on board
or at least aware of this movement in the fs land?

Added a few CC's for that.

								Honza

> Changes since v1:
>  - clean up a printk in gfs2
> 
> Diffstat:
>  fs/gfs2/aops.c         |   26 --------------------------
>  fs/gfs2/log.c          |    5 ++---
>  fs/iomap/buffered-io.c |   15 ---------------
>  fs/zonefs/super.c      |    8 --------
>  include/linux/iomap.h  |    3 ---
>  5 files changed, 2 insertions(+), 55 deletions(-)
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR