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SubjectRe: [TEST] page tables filling non-highmem


On Mon, 18 Feb 2002, Daniel Phillips wrote:

> On February 18, 2002 02:38 am, Andrea Arcangeli wrote:
> > On Fri, Feb 15, 2002 at 09:59:45AM +0100, Daniel Phillips wrote:
> > > On February 15, 2002 05:51 am, William Lee Irwin III wrote:
> > > > The following testcase brought down 2.4.17 mainline on an
> > > > 8-way P-III 700MHz machine with 12GB of RAM. The last thing
> > > > logged from it was a LowFree of 2MB with 9GB of highmem free
> > > > after something like 6-8 hours of pounding away, at which
> > > > time the machine stopped responding (IIRC it was given ~12
> > > > hours to echo another character).
> > > >
> > > > This testcase is a blatant attempt to fill the direct-mapped
> > > > portion of the kernel virtual address space with process pagetables.
> > > > It was suspected such a thing was happening in another failure scenario
> > > > which is what motivated me to devise this testcase. I believe a fix
> > > > already exists (i.e. aa's ptes in highmem stuff) though I've not yet
> > > > verified its correct operation here.
> > >
> > > As you described it to me on irc, this demonstration turns up a
> > > considerably worse problem than just having insufficient space for
> > > page tables - the system locks up hard instead of doing anything
> > > reasonable on page table-related oom. It's wrong that the system
> > > should behave this way, it is after all, just an oom.
> > >
> > > Now that basic stability issues seem to be under control, perhaps
> > > it's time to give the oom problem the attention it deserves?
> >
> > My tree doesn't lock up hard even without pte-highmem applied. The task
> > gets killed.
>
> Well, the obvious question is: Why Isn't It In Mainline???
>
> > backout pte-highmem, try the same testcase again on my tree
> > and you'll see. The oom handling in mainline is deadlock prone, I always
> > known this and that's why I always rejected it. Nobody but me
> > acklowledged this problem
>
> Lots of people acknowleged it, it seems just one guy fixed it.
>
> > and I spent quite an amount of time convincing
> > mainline maintainers about those deadlock flaws of the mainline approch
> > but I failed so I giveup waiting for a report like this, just like with
> > all the other stuff that is now in my vm patch, 90% of it I tried to
> > push it separately into mainline before having to accumulate it.
>
> What I'd suggest is, just post a list of each item outstanding item that
> haven't been pushed to mainline, and an explanation of which problem it
> fixes.
>
> Incorrect oom accounting has been a bleeding wound for well over a year,
> and if you've got a fix that's provably correct...
>
> Marcelo?? Is this just a stupid communication problem?

Andrew talked with me about merging parts of -aa VM into mainline.

I guess he will be doing the job during the 2.4.19-pre cycle. Am I right
Andrew?

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