1 May 2008 17:06
Re: [PATCH 0/8][for -mm] mem_notify v6
KOSAKI Motohiro <kosaki.motohiro <at> jp.fujitsu.com>
2008-05-01 15:06:05 GMT
2008-05-01 15:06:05 GMT
Hi Tom, > In my case of a Java virtual machine, where I originally saw the > problem, most of the code is interpreted byte codes or jit-compiled > native code, all of which resides not in the text segment but in > anonymous pages that aren't backed by a file, and there is no swap > space. The actual text segment working set can be very small (memory > allocation, garbage collection, synchronization, other random native > code). And, as KOSAKI Motohiro pointed out, it may be wise to mlock > these areas. So the text working set doesn't make an adequate > reserve. your memnotify check routine is written by native or java? if native, my suggestion is right. but if java, it is wrong. my point is "on swapless system, /dev/mem_notify checked routine should be mlocked". > However, I can maintain a reserve of cached and/or mapped memory by > touching pages in the text segment (or any mapped file) as the final > step of low memory notification handling, if the cached page count is > getting low. For my purposes, this is nearly the same as having an > additional threshold-based notification, since it forces notifications > to occur while the kernel still has some memory to satisfy allocations > while userspace code works to free memory. And it's simple. > > Unfortunately, this is more expensive than it could be since the pages > need to be read in from some device (mapping /dev/zero doesn't cause > pages to be allocated). What I'm looking for now is a cheap way to > populate the cache with pages that the kernel can throw away when it > needs to reclaim memory. I hope understand your requirement more. Can I ask your system more? I think all java text and data is mapped. When cached+mapped+free memory is happend? and at the time, What is used memory? Please don't think I have objection your proposal. merely, I don't understand your system yet. if I make new code before understand your requirement exactly, It makes many bug. IMHO threshold based notification has a problems. if low memory happend and application has no freeable memory, mem notification don't stop and increase CPU usage dramatically, but it is perfectly useless. I don't thin embedded java is not important, but I don't hope desktop regression...