Hi, > has there been any thoughts on utilizing posix_fadvise* in BackupPC?
thanks to the #linux IRC channel it's now clear that the kernel can and will evict cached dentries and inodes from RAM when files are read and written without using posix_fadvise, thus caching these files in the page cache. But here comes /proc/sys/vm/vfs_cache_pressure to the rescue: https://www.kernel.org/doc/Documentation/sysctl/vm.txt Controls the tendency of the kernel to reclaim the memory which is used for caching of directory and inode objects. At the default value of vfs_cache_pressure=100 the kernel will attempt to reclaim dentries and inodes at a "fair" rate with respect to pagecache and swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will never reclaim dentries and inodes due to memory pressure and this can easily lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100 causes the kernel to prefer to reclaim dentries and inodes. With my backuppc machine and its 96GB of RAM it's not usefull in my opinion that the dentries and inode data from e.g. the pool directory cached in RAM get's evicted because backuppc writes big files to disk not using posix_fadvise. So i will lower the value in /proc/sys/vm/vfs_cache_pressure from 100 to maybe 40 and see what happens. Regards Marcel ------------------------------------------------------------------------------ October Webinars: Code for Performance Free Intel webinars can help you accelerate application performance. Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from the latest Intel processors and coprocessors. See abstracts and register > http://pubads.g.doubleclick.net/gampad/clk?id=60135991&iu=/4140/ostg.clktrk _______________________________________________ BackupPC-users mailing list [email protected] List: https://lists.sourceforge.net/lists/listinfo/backuppc-users Wiki: http://backuppc.wiki.sourceforge.net Project: http://backuppc.sourceforge.net/
