Hello all, We are having some issues with some high throughput servers of ours. Here is the issue, we are using a vanilla 2.6.22.14 kernel on a node with 2 Dual Core Intels (3 GHz) and 16 GB of ram. The files that are being served are around 2 GB each, and there are usually 3 to 5 of them being read, so once read they fit into memory nicely, and when all is working correctly, we have a perfectly filled cache, with almost no disk activity. When we have large NFS activity (say, 600 to 1200 clients) connecting to the server(s), they can get into a state where they are using up all of memory, but they are dropping cache. slabtop is showing 13 GB of memory being used by the size-4096 slab object. We have two ethernet channels bonded, so we see in excess of 240 MB/s of data flowing out of the box, and all of the sudden, disk activity has risen to 185 MB/s. This happens if we are using 8 or more nfs threads. If we limit the threads to 6 or less, this doesn't happen. Of course, we are starving clients, but at least the jobs that my customers are throwing out there are progressing. The question becomes, what is causing the memory to be used up by the slab size-4096 object? Why when all of the sudden a bunch of clients ask for data does this object grow from 100 MB to 13 GB? I have set the memory settings to something that I thought was reasonable. Here is some more of the particulars: sysctl.conf tcp memory settings: # NFS Tuning Parameters sunrpc.udp_slot_table_entries = 128 sunrpc.tcp_slot_table_entries = 128 vm.overcommit_ratio = 80 net.core.rmem_max=524288 net.core.rmem_default=262144 net.core.wmem_max=524288 net.core.wmem_default=262144 net.ipv4.tcp_rmem = 8192 262144 524288 net.ipv4.tcp_wmem = 8192 262144 524288 net.ipv4.tcp_sack=0 net.ipv4.tcp_timestamps=0 vm.min_free_kbytes=50000 vm.overcommit_memory=1 net.ipv4.tcp_reordering=127 # Enable tcp_low_latency net.ipv4.tcp_low_latency=1 Here is a current reading from a slabtop of a system where this error is happening: 3007154 3007154 100% 4.00K 3007154 1 12028616K size-4096 Note the size of the object cache, usually it is 50 - 100 MB (I have another box with 32 threads and the same settings which is bouncing between 50 and 128 MB right now). I have a lot of client boxes that need access to these servers, and would really benefit from having more threads, but if I increase the number of threads, it pushes everything out of cache, forcing re-reads, and really slows down our jobs. Any thoughts on this? Thanks, Norman Weathers -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
