On Tue, Feb 27, 2024 at 9:20 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > On Tue 27-02-24 18:06:05, Yafang Shao wrote: > > On Tue, Feb 27, 2024 at 5:45 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > [...] > > > > Reclaiming numerous dentries through force_empty can also lead to > > > > potential issues, which is why we attempt to shrink the slab gradually > > > > to mitigate them. However, it's important to note that the underlying > > > > causes of the issues in force_empty and rmdir are not identical, as > > > > they involve different locks. > > > > > > Please be more specific about those issues. > > > > Both of these issues stem from lock contention: > > > > - rmdir > > When executing rmdir, the lock of the inode of the empty directory is > > held. If this directory contains numerous negative dentries, this lock > > is held for an extended duration. Consequently, if other processes > > attempt to acquire this lock, they are blocked. > > A simple reproducer involves: > > > > 1. Generating numerous negative dentries in an empty directory. > > 2. Running `rmdir ~/test` and `ls ~/` concurrently. > > I fail to see how is this relevant to memcg reclaim It appears there might still be some misunderstanding regarding the issue at hand. The numerous negative dentries are generated within a memcg. I simplified the explanation by omitting the memcg context. > > > This setup demonstrates that ls takes a significant amount of time to > > complete due to lock contention. > > > > - force_empty > > Force_empty holds the lock of super_block->dentry_list. However, I > > haven't yet had the opportunity to produce a specific example to > > illustrate this issue. > > OK, get back to us once you can identify an actual problem. We might be Pls. take a look at the force_empty->prune_dcache_sb->shrink_dentry_list. > talking about different things here though. My question is directed at > existing memcg interfaces to reclaim the memory. That would be legacy > (and effectively deprecated) force_empty and memory.reclaim that we > have. -- Regards Yafang
