[PATCH v2 0/5] kdump: crashkernel reservation from CMA
Michal Hocko
mhocko at suse.com
Fri May 30 02:26:06 PDT 2025
On Fri 30-05-25 11:11:40, David Hildenbrand wrote:
> On 30.05.25 11:07, Michal Hocko wrote:
> > On Fri 30-05-25 10:39:39, David Hildenbrand wrote:
> > > On 30.05.25 10:28, Michal Hocko wrote:
> > [...]
> > > > All that being said I would go with an additional parameter to the
> > > > kdump cma setup - e.g. cma_sane_dma that would skip waiting and use 10s
> > > > otherwise. That would make the optimized behavior opt in, we do not need
> > > > to support all sorts of timeouts and also learn if this is not
> > > > sufficient.
> > > >
> > > > Makes sense?
> > >
> > > Just so I understand correctly, you mean extending the "crashkernel=" option
> > > with a boolean parameter? If set, e.g., wait 1s, otherwise magic number 10?
> >
> > crashkernel=1G,cma,cma_sane_dma # no wait on transition
>
> But is no wait ok? I mean, any O_DIRECT with any device would at least take
> a bit, no?
>
> Of course, there is a short time between the crash and actually triggerying
> kdump.
This is something we can test for and if we need a short timeout in this
case as well then it is just trivial to add it. I am much more
concerned about those potentially unpredictable DMA transfers that could
take too long and it is impossible to test for those and therefore we
need to overshoot.
> > crashkernel=1G,cma # wait on transition with e.g. 10s timeout
>
> In general, would work for me.
>
> --
> Cheers,
>
> David / dhildenb
--
Michal Hocko
SUSE Labs
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