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SubjectRe: [PATCH v2 0/5] clean up and generalize swap-over-NFS
On Tue, Jan 13, 2015 at 07:18:36PM -0800, Omar Sandoval wrote:
> 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

Hi,

Any updates on this?

Thanks,
--
Omar


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