From: Trond Myklebust <trond.myklebust@primarydata.com>
To: Chuck Lever <chuck.lever@oracle.com>, linux-nfs@vger.kernel.org
Subject: [PATCH 00/20] Reducing inode->i_lock contention in writebacks
Date: Wed, 19 Jul 2017 18:09:35 -0400
Message-Id: <20170719220955.58210-1-trond.myklebust@primarydata.com>
Sender: linux-nfs-owner@vger.kernel.org

Chuck Lever has presented measurements, that would appear to indicate that
the inode->i_lock can be a source of contention when doing writeback using
high performance networks. This patch series is therefore an attempt to
address the sources of contention that his measurements pointed to.

According to Chuck's table, the main sources of contention appear to
be in nfs_flush_incompatible(), nfs_lock_and_join_requests() and
nfs_updatepage(). Most of this patch series focuses on fixing
nfs_lock_and_join_requests(), since it holds the inode lock, while
taking locks on the page group and the sub-requests themselves,
rolling them all back if ever there is contention.
By noting a few simple rules that are mostly already in place, we
can simplify that locking to ensure that we only have to keep the
spin lock while we're dereferencing and locking the head page pointer
that is stored in page_private(page).

Along the way, the patches also simplify the code a little, and fix
a number of subtle races which mainly occur when you set wsize to
some value smaller than the page size. The most notable such race
occurs between nfs_lock_and_join_requests() and nfs_page_group_destroy(),
and could lead to a double free() of some of the sub-requests.

Finally, there are 2 patches tacked onto the end of the series that
attempt to improve the throttling of writes when the RPC layer is
congested. They do so by forcing each caller of nfs_initiate_pgio()
to wait until the request is being transmitted. The expectation is
that this might help improve latencies when there are several processes
competing for access to the RPC transport.

Trond Myklebust (20):
  NFS: Simplify page writeback
  NFS: Reduce lock contention in nfs_page_find_head_request()
  NFS: Reduce lock contention in nfs_try_to_update_request()
  NFS: Ensure we always dereference the page head last
  NFS: Fix a reference and lock leak in nfs_lock_and_join_requests()
  NFS: Fix an ABBA issue in nfs_lock_and_join_requests()
  NFS: Don't check request offset and size without holding a lock
  NFS: Don't unlock writebacks before declaring PG_WB_END
  NFS: Fix the inode request accounting when pages have subrequests
  NFS: Teach nfs_try_to_update_request() to deal with request
    page_groups
  NFS: Remove page group limit in nfs_flush_incompatible()
  NFS: Reduce inode->i_lock contention in nfs_lock_and_join_requests()
  NFS: Further optimise nfs_lock_and_join_requests()
  NFS: Fix nfs_page_group_destroy() and nfs_lock_and_join_requests()
    race cases
  NFS: Remove nfs_page_group_clear_bits()
  NFS: Remove unuse function nfs_page_group_lock_wait()
  NFS: Remove unused parameter from nfs_page_group_lock()
  NFS: Fix up nfs_page_group_covers_page()
  SUNRPC: Add a function to allow waiting for RPC transmission
  NFS: Throttle I/O to the NFS server

 fs/nfs/pagelist.c            |  64 +++------
 fs/nfs/write.c               | 313 ++++++++++++++++++-------------------------
 include/linux/nfs_page.h     |   3 +-
 include/linux/sunrpc/sched.h |   3 +
 net/sunrpc/sched.c           |  22 +++
 net/sunrpc/xprt.c            |   6 +
 6 files changed, 177 insertions(+), 234 deletions(-)

-- 
2.13.3