Pre-populating anonymous pages

By: Linus Torvalds (torvalds.delete@this.linux-foundation.org), June 18, 2019 4:28 pm
Room: Moderated Discussions
Travis Downs (travis.downs.delete@this.gmail.com) on June 17, 2019 9:18 am wrote:
>
> Before Meltdown the "fault in" speed limit used to
> be closer to 10 GB/s, so I guess the fault time used to be closer to 400 ns. That is roughly consistent,
> if a bit slower, with syscall slowdown I observed after spec + melt.

Note that while I find meltdown hugely annoying, I also personally treat it as a temporary annoyance rather than something I should worry about "design wise".

You can already avoid the Meltdown performance issue by various methods: either just go AMD, or by having a newer Intel CPU (although the whole MDS debacle means that even current Intel CPU's just have another system call and page fault slowdown instead).

Or you might even just decide that Meltdown and MDS aren't issues for your particular loads, and boot with "mitigation=off". For a lot of "private workstation" situations (or for "trusted server" cases, of course), that's probably quite reasonable, even if it does require more of an active decision on how you feel about the hw security model.

Basically I feel that the slowdown in page fault handling is something that should be treated as "you have bad hardware". We've been in that situation before: the Intel netburst architecture had some horrendous fault latencies too (albeit for different reasons), and I complained about those. They eventually went away, and now it's just a bad memory.

So I really don't want to make any kernel architectural design decisions based on "current hardware has some random issues".

That said, it probably would be interesting to look at just doing fault-around for anonymous pages too. I'll think about it in my copious spare time.

Linus
< Previous Post in Thread 
TopicPosted ByDate
Pre-populating anonymous pagesTravis Downs2019/06/05 04:48 PM
  Pre-populating anonymous pagesJeff S.2019/06/05 08:03 PM
    Pre-populating anonymous pagesTravis Downs2019/06/06 07:11 AM
      Pre-populating anonymous pagesJeff S.2019/06/06 08:40 AM
        Pre-populating anonymous pagesTravis Downs2019/06/06 08:59 AM
          Pre-populating anonymous pagesJeff S.2019/06/06 09:19 AM
  Pre-populating anonymous pagesFoo_2019/06/06 12:30 AM
    Pre-populating anonymous pagesTravis Downs2019/06/06 06:59 AM
      Pre-populating anonymous pagesFoo_2019/06/06 07:56 AM
        Pre-populating anonymous pagesTravis Downs2019/06/06 09:02 AM
  Pre-populating anonymous pagesLinus Torvalds2019/06/06 11:01 AM
    Pre-populating anonymous pagesTravis Downs2019/06/07 02:16 PM
      Pre-populating anonymous pagesBrendan2019/06/08 02:55 AM
        Pre-populating anonymous pagesTravis Downs2019/06/08 08:18 AM
        Pre-populating anonymous pagesLinus Torvalds2019/06/08 11:43 AM
          Pre-populating anonymous pagesBrendan2019/06/09 03:29 AM
            Pre-populating anonymous pagesLinus Torvalds2019/06/10 11:20 AM
          Pre-populating anonymous pagesTravis Downs2019/06/17 09:18 AM
            Pre-populating anonymous pagesLinus Torvalds2019/06/18 04:28 PM
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