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

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

On 2026/2/27 16:27, Muchun Song wrote:
>
>
>> On Feb 27, 2026, at 16:17, yebin (H) <yebin10@huawei.com> wrote:
>>
>>
>>
>> On 2026/2/27 15:45, Muchun Song wrote:
>>>
>>>
>>>> On Feb 27, 2026, at 15:32, yebin (H) <yebin10@huawei.com> wrote:
>>>>
>>>>
>>>>
>>>> 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.
>>>
>>> If the inode is evicted, the page cache is evicted as well. It cannot evict page
>>> cache alone. Why you want to evict cache alone?
>>>
>> The condition for dentry/inode to be reclaimed is that there are no
>> references to them. Therefore, relying on inode reclamation for page
>> cache reclamation has limitations. Additionally, there is currently no
>
> What limit?
>
If the file is occupied, the page cache cannot be reclaimed through
inode reclamation.
>> usage statistics for the page cache based on a single file system. By
>> comparing the page cache usage before and after reclamation, we can
>> roughly estimate the amount of page cache used by a file system.
>
> I'm curious why dropping inodes doesn't show a noticeable difference
> in page cache usage before and after?
>
>>
>>>>>>
>>>>>> 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
>>>>>>>>
>>>>>>>
>>>>>>> .
>>>>>>>
>>>>>
>>>>> .
>>>
>>>
>>>
>>>
>>> .
>
>
> .
>