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

[Muchun Song <muchun.song@linux.dev>]

> 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.

> 
> 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
>>> 
>> 
>> .
>>