Messages in this thread | | | Date | Wed, 02 Apr 2008 16:31:27 +0900 | From | KOSAKI Motohiro <> | Subject | Re: [PATCH 0/8][for -mm] mem_notify v6 |
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Hi Tom,
Thank you very useful comment. that is very interesting.
> I tried it with a real-world program that, among other things, mmaps > anonymous pages and touches them at a reasonable speed until it gets > notified via /dev/mem_notify, releases most of them with > madvise(MADV_DONTNEED), then loops to start the cycle again. > > What tends to happen is that I do indeed get notifications via > /dev/mem_notify when the kernel would like to be swapping, at which > point I free memory. But the notifications come at a time when the > kernel needs memory, and it gets the memory by discarding some Cached > or Mapped memory (I can see these decreasing in /proc/meminfo with > each notification). With each mmap/notify/madvise cycle the Cached > and Mapped memory gets smaller, until eventually while I'm touching > pages the kernel can't find enough memory and will either invoke the > OOM killer or return ENOMEM from syscalls. This is precisely the > situation I'm trying to avoid by using /dev/mem_notify.
Could you send your test program? I can't reproduce that now, sorry.
> The criterion of "notify when the kernel would like to swap" feels > correct, but in addition I seem to need something like "notify when > cached+mapped+free memory is getting low".
Hmmm, I think this idea is only useful when userland process call madvise(MADV_DONTNEED) periodically.
but I hope improve my patch and solve your problem. if you don' mind, please help my testing ;)
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