You can also use vm.lower_zone_protection=size_in_mb to protect portions of low memory. This doesn't help with caching issues but can help prevent the kernel from getting cornered and resorting to oom-killer. We haven't tested everything in our enviroment at 64bit so we've used lower zone protection to give the kernel buffers some working space. This becomes an issue under 32bit kernels when attempting disk and network IO at Gig speeds. It also forces more of the page cache to high memory. Paul On Tue, 9 Oct 2007, Andrew Morgan wrote: > On Sat, 6 Oct 2007, Rob Mueller wrote: > > > As it turns out, the memory leaks weren't critical, because the the pages do > > seem to be reclaimed when needed, though it was annoying not knowing exactly > > how much memory was really free/used. The biggest problem was that with > > cyrus you have millions of small files, and with a 32bit linux kernel the > > inode cache has to be in low memory, severely limiting how many files the OS > > will cache. > > > > See this blog post for the gory details, and why a 64-bit kernel was a nice > > win for us. > > > > http://blog.fastmail.fm/2007/09/21/reiserfs-bugs-32-bit-vs-64-bit-kernels-cache-vs-inode-memory/ > > Yesterday I checked my own Cyrus servers to see if I was running out of > lowmem, and it sure looked like it. Lowmem had only a couple MB free, and > I had 2GB of free memory that was not being used for cache. > > I checked again today and everything seems to be fine - 150MB of lowmem > free and almost no free memory (3GB cached)! Grrr. > > Anyways, I was looking into building a 64-bit kernel. I'm running Debian > Sarge (I know, old) on a Dell 2850 with Intel Xeon (Nocona) CPUs and 4GB > RAM. My kernel version is 2.6.14.5, built from kernel.org sources. It > has "High Memory Support (64GB)" selected. > > When I run menuconfig, I'm not seeing any obvious place to switch from > 32-bit to 64-bit. Could you elaborate a bit about how you switched to a > 64-bit kernel? Also, are you running a full 64-bit distro, or just a > 64-bit kernel? > > Thanks, > Andy > ---- > Cyrus Home Page: http://cyrusimap.web.cmu.edu/ > Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki > List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html > ---- Cyrus Home Page: http://cyrusimap.web.cmu.edu/ Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
