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

From: Waiman Long
Date: Tue Aug 15 2017 - 13:15:22 EST


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