On Fri, Dec 19, 2014 at 07:18:24PM -0800, Omar Sandoval wrote: > Hi, > > This patch series (based on ecb5ec0 in Linus' tree) contains all of the > non-BTRFS work that I've done to implement swapfiles on BTRFS. The BTRFS > portion is still undergoing development and is now outweighed by the > non-BTRFS changes, so I want to get these in separately. > > Version 2 changes the generic swapfile interface to use ->read_iter and > ->write_iter instead of using ->direct_IO directly in response to > discussion on the previous submission. It also adds the iov_iter_is_bvec > helper to factor out some common checks. > > Version 1 can be found here: https://lkml.org/lkml/2014/12/15/7 > > Omar Sandoval (5): > iov_iter: add ITER_BVEC helpers > direct-io: don't dirty ITER_BVEC pages on read > nfs: don't dirty ITER_BVEC pages read through direct I/O > swapfile: use ->read_iter and ->write_iter > vfs: update swap_{,de}activate documentation > > Documentation/filesystems/Locking | 7 ++++--- > Documentation/filesystems/vfs.txt | 7 ++++--- > fs/direct-io.c | 8 ++++--- > fs/nfs/direct.c | 5 ++++- > fs/splice.c | 7 ++----- > include/linux/uio.h | 7 +++++++ > mm/iov_iter.c | 12 +++++++++++ > mm/page_io.c | 44 +++++++++++++++++++++++++-------------- > mm/swapfile.c | 11 +++++++++- > 9 files changed, 76 insertions(+), 32 deletions(-) > > -- > 2.2.1 > Hi, everyone, Thanks for all of the feedback on the last few iterations of this series. If it's alright, I'd like to revive the conversation around these patches. There are a couple of issues which we were discussing before the holidays: One concern that Al mentioned was ->read_iter and ->write_iter falling back to the buffered I/O case. Like Christoph mentioned, this can be prevented by doing the proper checks on the filesystem side (usually just making sure that all blocks of a swapfile are allocated, but on BTRFS, for example, we also have to check for compressed extents). The other concern which Al brought up was that ->read_iter is passed a locked page in the iter_bvec and could end up trying to lock it. I'm not too sure under what conditions that would happen -- could someone give an example? My intuition is that there's no path which will lead us to deadlock on a page in the swapcache, but I don't have anything solid to back that up. Thanks! -- Omar -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>