Re: [PATCH v3 0/3] add support for drop_caches for individual filesystem

["yebin (H)" <yebin10@huawei.com>]

On 2026/2/27 14:55, Muchun Song wrote:
>
>
>> On Feb 27, 2026, at 14:39, yebin (H) <yebin10@huawei.com> wrote:
>>
>>
>>
>> On 2026/2/27 11:31, Muchun Song wrote:
>>>
>>>
>>>> On Feb 27, 2026, at 10:55, Ye Bin <yebin@huaweicloud.com> wrote:
>>>>
>>>> From: Ye Bin <yebin10@huawei.com>
>>>>
>>>> In order to better analyze the issue of file system uninstallation caused
>>>> by kernel module opening files, it is necessary to perform dentry recycling
>>>> on a single file system. But now, apart from global dentry recycling, it is
>>>> not supported to do dentry recycling on a single file system separately.
>>>
>>> Would shrinker-debugfs satisfy your needs (See Documentation/admin-guide/mm/shrinker_debugfs.rst)?
>>>
>>> Thanks,
>>> Muchun
>>>
>> Thank you for the reminder. The reclamation of dentries and nodes can meet my needs. However, the reclamation of the page cache alone does not satisfy my requirements. I have reviewed the code of shrinker_debugfs_scan_write() and found that it does not support batch deletion of all dentries/inode for all nodes/memcgs,instead, users need to traverse through them one by one, which is not very convenient. Based on my previous experience, I have always performed dentry/inode reclamation at the file system level.
>
> I don't really like that you're implementing another mechanism with duplicate
> functionality. If you'd like, you could write a script to iterate through them
> and execute it that way—I don't think that would be particularly inconvenient,
> would it? If the iteration operation of memcg is indeed quite cumbersome, I
> think extending the shrinker debugfs functionality would be more appropriate.
>
The shrinker_debugfs can be extended to support node/memcg/fs 
granularity reclamation, similar to the extended function of echo " 0 - 
X" > count /echo " - 0 X" > count /echo " - - X" > count. This only 
solves the problem of reclaiming dentries/inode based on a single file 
system. However, the page cache reclamation based on a single file 
system cannot be implemented by using shrinker_debugfs. If the extended 
function is implemented by shrinker_debugfs, drop_fs_caches can reuse 
the same interface and maintain the same semantics as drop_caches.
>>
>> Thanks,
>> Ye Bin
>>>> This feature has usage scenarios in problem localization scenarios.At the
>>>> same time, it also provides users with a slightly fine-grained
>>>> pagecache/entry recycling mechanism.
>>>> This patchset supports the recycling of pagecache/entry for individual file
>>>> systems.
>>>>
>>>> Diff v3 vs v2
>>>> 1. Introduce introduce drop_sb_dentry_inode() helper instead of
>>>> reclaim_dcache_sb()/reclaim_icache_sb() helper for reclaim dentry/inode.
>>>> 2. Fixing compilation issues in specific architectures and configurations.
>>>>
>>>> Diff v2 vs v1:
>>>> 1. Fix possible live lock for shrink_icache_sb().
>>>> 2. Introduce reclaim_dcache_sb() for reclaim dentry.
>>>> 3. Fix potential deadlocks as follows:
>>>> https://lore.kernel.org/linux-fsdevel/00000000000098f75506153551a1@google.com/
>>>> After some consideration, it was decided that this feature would primarily
>>>> be used for debugging purposes. Instead of adding a new IOCTL command, the
>>>> task_work mechanism was employed to address potential deadlock issues.
>>>>
>>>> Ye Bin (3):
>>>>   mm/vmscan: introduce drop_sb_dentry_inode() helper
>>>>   sysctl: add support for drop_caches for individual filesystem
>>>>   Documentation: add instructions for using 'drop_fs_caches sysctl'
>>>>     sysctl
>>>>
>>>> Documentation/admin-guide/sysctl/vm.rst |  44 +++++++++
>>>> fs/drop_caches.c                        | 125 ++++++++++++++++++++++++
>>>> include/linux/mm.h                      |   1 +
>>>> mm/internal.h                           |   3 +
>>>> mm/shrinker.c                           |   4 +-
>>>> mm/vmscan.c                             |  50 ++++++++++
>>>> 6 files changed, 225 insertions(+), 2 deletions(-)
>>>>
>>>> --
>>>> 2.34.1
>>>>
>>>
>>> .
>>>
>
> .
>