linux-kernel - [PATCH v3 0/5] fs/dcache: Limit # of negative dentries

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Message-Id: <1501266880-26288-1-git-send-email-longman@redhat.com>
Date:   Fri, 28 Jul 2017 14:34:35 -0400
From:   Waiman Long <longman@...hat.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Jonathan Corbet <corbet@....net>
Cc:     linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Larry Woodman <lwoodman@...hat.com>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH v3 0/5] fs/dcache: Limit # of negative dentries

 v2->v3:
  - Add a faster pruning rate when the free pool is closed to depletion.
  - As suggested by James Bottomley, add an artificial delay waiting
    loop before killing a negative dentry and properly clear the
    DCACHE_KILL_NEGATIVE flag if killing doesn't happen.
  - Add a new patch to track number of negative dentries that are
    forcifully killed.

 v1->v2:
  - Move the new nr_negative field to the end of dentry_stat_t structure
    as suggested by Matthew Wilcox.
  - With the help of Miklos Szeredi, fix incorrect locking order in
    dentry_kill() by using lock_parent() instead of locking the parent's
    d_lock directly.
  - Correctly account for positive to negative dentry transitions.
  - Automatic pruning of negative dentries will now ignore the reference
    bit in negative dentries but not the regular shrinking.

A rogue application can potentially create a large number of negative
dentries in the system consuming most of the memory available. This
can impact performance of other applications running on the system.

This patchset introduces changes to the dcache subsystem to limit
the number of negative dentries allowed to be created thus limiting
the amount of memory that can be consumed by negative dentries.

Patch 1 tracks the number of negative dentries used and disallow
the creation of more when the limit is reached.

Patch 2 enables /proc/sys/fs/dentry-state to report the number of
negative dentries in the system.

Patch 3 enables automatic pruning of negative dentries when it is
close to the limit so that we won't end up killing recently used
negative dentries.

Patch 4 prevents racing between negative dentry pruning and umount
operation.

Patch 5 shows the number of forced negative dentry killings in
/proc/sys/fs/dentry-state. End users can then tune the neg_dentry_pc=
kernel boot parameter if they want to reduce forced negative dentry
killings.

Waiman Long (5):
  fs/dcache: Limit numbers of negative dentries
  fs/dcache: Report negative dentry number in dentry-state
  fs/dcache: Enable automatic pruning of negative dentries
  fs/dcache: Protect negative dentry pruning from racing with umount
  fs/dcache: Track count of negative dentries forcibly killed

 Documentation/admin-guide/kernel-parameters.txt |   7 +
 fs/dcache.c                                     | 451 ++++++++++++++++++++++--
 include/linux/dcache.h                          |   8 +-
 include/linux/list_lru.h                        |   1 +
 mm/list_lru.c                                   |   4 +-
 5 files changed, 435 insertions(+), 36 deletions(-)

-- 
1.8.3.1