Re: [PATCH mm] vmalloc: back off when the current task is OOM-killed

[Andrew Morton]

On Mon, 20 Sep 2021 13:59:35 +0300 Vasily Averin <vvs@xxxxxxxxxxxxx> wrote:

> On 9/20/21 4:22 AM, Tetsuo Handa wrote:
> > On 2021/09/20 8:31, Andrew Morton wrote:
> >> On Fri, 17 Sep 2021 11:06:49 +0300 Vasily Averin <vvs@xxxxxxxxxxxxx> wrote:
> >>
> >>> Huge vmalloc allocation on heavy loaded node can lead to a global
> >>> memory shortage. A task called vmalloc can have the worst badness
> >>> and be chosen by OOM-killer, however received fatal signal and
> >>> oom victim mark does not interrupt allocation cycle. Vmalloc will
> >>> continue allocating pages over and over again, exacerbating the crisis
> >>> and consuming the memory freed up by another killed tasks.
> >>>
> >>> This patch allows OOM-killer to break vmalloc cycle, makes OOM more
> >>> effective and avoid host panic.
> >>>
> >>> Unfortunately it is not 100% safe. Previous attempt to break vmalloc
> >>> cycle was reverted by commit b8c8a338f75e ("Revert "vmalloc: back off when
> >>> the current task is killed"") due to some vmalloc callers did not handled
> >>> failures properly. Found issues was resolved, however, there may
> >>> be other similar places.
> >>
> >> Well that was lame of us.
> >>
> >> I believe that at least one of the kernel testbots can utilize fault
> >> injection.  If we were to wire up vmalloc (as we have done with slab
> >> and pagealloc) then this will help to locate such buggy vmalloc callers.
> 
> Andrew, could you please clarify how we can do it?
> Do you mean we can use exsiting allocation fault injection infrastructure to trigger
> such kind of issues? Unfortunately I found no ways to reach this goal.
> It  allows to emulate single faults with small probability, however it is not enough,
> we need to completely disable all vmalloc allocations. 

I don't see why there's a problem?  You're saying "there might still be
vmalloc() callers which don't correctly handle allocation failures",
yes?

I'm suggesting that we use fault injection to cause a small proportion
of vmalloc() calls to artificially fail, so such buggy callers will
eventually be found and fixed.  Why does such a scheme require that
*all* vmalloc() calls fail?