On Thu, Jul 28, 2022 at 01:10:16PM +0200, Jan Kara wrote: > 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? I mentioned it during my folio session at LSFMM, but didn't put a huge emphasis on it. For XFS, writeback should already be in progress on other pages if we're getting to the point of trying to call ->writepage() in vmscan. Surely this is also true for other filesystems?
