Hello, We have a bunch of servers that create a lot of temp files, or check for the existence of non-existent files. Every such operation creates a dentry object and soon most of the free memory is consumed for 'negative' dentry entries. This behavior was observed on both CentOS kernel v.2.6.32-358 and Amazon Linux kernel v.3.4.43-4. There are also some processes running that occasionally allocate large chunks of memory, and when this happens the kernel clears out a bunch of stale dentry caches. This clearing takes some time. kswapd kicks in, and allocations and bzero() of 4GB that normally takes <1s, takes 20s or more. Because the memory needs are non-continuous but negative dentry generation is fairly continuous, vfs_cache_pressure doesn't help much. The thought I had was to have a sysctl that limits the number of dentries per super-block (sb-max-dentry). Everytime a new dentry is allocated in d_alloc(), check if dentry_stat.nr_dentry exceeds (number of super blocks * sb-max-dentry). If yes, queue up an asynchronous workqueue call to prune_dcache(). Also have a separate sysctl to indicate by what percentage to reduce the dentry entries when this happens. Thanks for your input. If this sounds like a reasonable idea, I'll send out a patch. Cheers, Keyur. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
