On Wed 18-02-15 19:44:06, Cheng Rk wrote: > > > On Wednesday, February 18, 2015 6:23 AM, Michal Hocko <mhocko@xxxxxxx> wrote: > On Fri 13-02-15 09:52:16, Cheng Rk wrote: > > > As per Documentation/sysctl/vm.txt the knob doesn't affect the page > > cache reclaim but rather inode vs. dentry reclaim. > > > So do you think is it worth to work on something to give pressure similar > to vm.vfs_cache_pressure to vfs inode & dentry cache? > > I am looking for an effect to let the kernel more aggressively reclaim > memory from Buffers, more aggressively than what? Anonymous memory, other types of caches? To be honest I do not see why we should treat buffers any different from any other cache. So far it is not clear what might be the issue you are seeing but I would suspect that too many buffers is not the primary one. It is hard to say anything more without any specific numbers, though. > By reading fs/super.c:prune_super I've also realized taht, which is the > only place referening sysctl_vfs_cache_pressure, > that block_devices' inode are in "bdev" mount, its super_block just > have nr_cached_objects as NULL, > s_nr_dentry_unused and s_nr_inodes_unused both 0, get total_objects to be > reclaimed is 0; > > So is why sysctl_vfs_cache_pressure doesn't give pressure to Buffers, > > > if (sb->s_op && sb->s_op->nr_cached_objects) > fs_objects = sb->s_op->nr_cached_objects(sb); > > total_objects = sb->s_nr_dentry_unused + > sb->s_nr_inodes_unused + fs_objects; > > total_objects = (total_objects / 100) * sysctl_vfs_cache_pressure; > drop_super(sb); > > > In crash, I got to know this block_device (253:2, or /dev/dm-2)has > 10536805 pages mapped, that is the 40GB memory in Buffers, I still do not see why is that a problem. They should get reclaimed on demand. > I wonder is there a sysctl can controll this to be reclaimed earlier? I do not know about any. [...] -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>