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

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Message-ID: <1cdfb670-42ed-f8f6-aeab-c38ea0567651@redhat.com>
Date:   Tue, 15 Aug 2017 13:15:13 -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>
Subject: Re: [PATCH v3 0/5] fs/dcache: Limit # of negative dentries

On 07/28/2017 02:34 PM, Waiman Long wrote:
>  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(-)
>
I haven't received any comment on this v3 patch for over 2 weeks. Is
there anything I can do to make it more ready to be merged?

Thanks,
Longman