On Sat 25-06-22 11:11:43, Christoph Hellwig wrote: > On Fri, Jun 24, 2022 at 03:07:50PM +0200, Jan Kara wrote: > > I'm not sure I get the context 100% right but pages getting randomly dirty > > behind filesystem's back can still happen - most commonly with RDMA and > > similar stuff which calls set_page_dirty() on pages it has got from > > pin_user_pages() once the transfer is done. page_maybe_dma_pinned() should > > be usable within filesystems to detect such cases and protect the > > filesystem but so far neither me nor John Hubbart has got to implement this > > in the generic writeback infrastructure + some filesystem as a sample case > > others could copy... > > Well, so far the strategy elsewhere seems to be to just ignore pages > only dirtied through get_user_pages. E.g. iomap skips over pages > reported as holes, and ext4_writepage complains about pages without > buffers and then clears the dirty bit and continues. > > I'm kinda surprised that btrfs wants to treat this so special > especially as more of the btrfs page and sub-page status will be out > of date as well. I agree btrfs probably needs a different solution than what it is currently doing if they want to get things right. I just wanted to make it clear that the code you are ripping out may be a wrong solution but to a real problem. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
