Hi, On Mon, Sep 26, 2011 at 6:24 PM, Christoph Lameter <cl@xxxxxxxxxx> wrote: > On Mon, 26 Sep 2011, Gilad Ben-Yossef wrote: > >> I do not know if these scenarios warrant the additional overhead, >> certainly not in all situations. Maybe the right thing is to make it a >> config option dependent. As I stated in the patch description, that is >> one of the thing I'm interested in feedback on. > > The flushing of the per cpu pages only done when kmem_cache_shrink() is > run or when a slab cache is closed. And for diagnostics. So its rare and > not performance critical. Yes, I understand. The problem is it pops up in the oddest of place. An example is in order: The Ipath Infiniband hardware exports a char device interface to user space. When a user opens the char device and configures a port, a kmem_cache is created. When the user later closes the fd, the release method of the char device destroys the kmem_cache. So, if I have some high performance server with 128 processors, and I've dedicated 127 processors to run my CPU bound computing tasks (and made sure the interrupt are serviced by the last CPU) and then run a shell on the lone admin CPU to do a backup, I can interrupt my 127 CPUs doing computational tasks, even though they have nothing to do with Infiniband, or backup and have never allocated a single buffer form that cache. I believe there is a similar scenario with software raid if I change RAID configs and several other places. In fact, I'm guessing many of the lines that pop up when doing the following grep hide a similar scenario: $ git grep kmem_cache_destroy . | grep '\->' I hope this explains my interest. My hope is to come up with a way to do more code on the CPU doing the flush_all (which as you said is a rare and none performance critical code path anyway) and by that gain the ability to do the job without interrupting CPUs that do not need to flush their per cpu pages. Thanks, Gilad > > > -- Gilad Ben-Yossef Chief Coffee Drinker gilad@xxxxxxxxxxxxx Israel Cell: +972-52-8260388 US Cell: +1-973-8260388 http://benyossef.com "I've seen things you people wouldn't believe. Goto statements used to implement co-routines. I watched C structures being stored in registers. All those moments will be lost in time... like tears in rain... Time to die. " -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>