Messages in this thread | | | Date | Mon, 21 Apr 2008 13:32:06 -0700 | From | "Tom May" <> | Subject | Re: [PATCH 0/8][for -mm] mem_notify v6 |
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On Fri, Apr 18, 2008 at 3:07 AM, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> I investigated again and found 2 problem in your test program. > > 1. text segment isn't locked. > > if strong memory pressure happned, kernel may drop program text region. > then your test program suddenly slow down. > > please use mlockall(MCL_CURRENT) before large buffer allocation.
Using mlock does enable the program to respond faster (and/or the kernel doesn't have to find memory to fault the page in) and solves the problem for this simple test program. I think we're thinking of the solution in two different ways: you want the program to react more quickly or be "nicer", and I want the kernel to give notification early enough to allow time for things that can (and do) happen when things aren't so nice. I realize that in extreme circumstances oom may be unavoidable, but a threshold-based notification, in addition to the current /dev/mem_notify mechanism, would help avoid extreme circumstances. I'm going to look into doing this.
> 2. repeat open/close to /proc/meminfo. > > in the fact, open(2) system call use a bit memory. > if call open(2) in strong memory pressure, doesn't return until > memory freed enough. > thus, it cause slow down your program sometimes.
This should be fine; I intentionally do the open/read/write/close after freeing memory.
> attached changed test program :) > it works well on my test environment.
I made your changes to my program (I'm using clone since I don't have a pthreads library on my device, and I left PAGESIZE at 4K instead of 64K), and having memory locked does avoid oom in this case, but unfortunately I don't think it's a general solution that will work everywhere in my system. (Although I'm going to try it.)
Thanks, .tom
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