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

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Message-ID: <87B246BB5ED53A4C98E4F9A35839EDE1853965F7@nkgeml514-mbx.china.huawei.com>
Date:   Wed, 16 Aug 2017 10:33:41 +0000
From:   "Wangkai (Kevin,C)" <wangkai86@...wei.com>
To:     Waiman Long <longman@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jonathan Corbet <corbet@....net>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-fsdevel@...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

> -----Original Message-----
> From: linux-fsdevel-owner@...r.kernel.org
> [mailto:linux-fsdevel-owner@...r.kernel.org] On Behalf Of Waiman Long
> Sent: Wednesday, August 16, 2017 1:15 AM
> To: Alexander Viro; Jonathan Corbet
> Cc: linux-kernel@...r.kernel.org; linux-doc@...r.kernel.org;
> linux-fsdevel@...r.kernel.org; Paul E. McKenney; Andrew Morton; Ingo Molnar;
> Miklos Szeredi; Matthew Wilcox; Larry Woodman; James Bottomley
> 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

Hi Longman,
I am a fresher of fsdevel, about 2 weeks before, I have joined this mail list, recently I have met the same problem of negative dentries, 
in my opinion, the dentries should be remove together with the files or directories, I don't know you have submit this patch, I have
another patch about this:

http://marc.info/?l=linux-fsdevel&m=150209902215266&w=2

maybe this is a foo idea...

regards
Kevin