Re: [PATCH] mm/page_alloc: do not boost watermarks in kdump capture kernels

[Yuanhe Shu <xiangzao@linux.alibaba.com>]

On 9/15/26 14:02, Vlastimil Babka wrote:
> Sounds like an oversight and we should deboost watermarks first before going
> for an oom kill? But I guess at the same time not boosting in the first
> place in kdump capture kernels makes sense and it's simpler to do.

Agreed. Deboosting before the OOM kill does look like a separate fix
worth doing, but it would change the OOM path for normal kernels too, so
this patch stays limited to the capture kernel.

> Hm while the large pageblocks on 64kb kernels are source of various
> surprises, this at least seems consistent to me. The check together with the
> clamp means we limit the boost to 1/4 of the zone regardless of pageblock
> size, right?

Yes: the check gives pageblock_nr_pages <= zone_managed_pages/4, and with
the large pageblocks here the clamp caps a single boost at one pageblock,
so watermark_boost <= pageblock_nr_pages <= zone_managed_pages/4.

> We should stop mentioning kdump capture kernels here then? They can't reach
> here anymore.

Right, capture kernels now return earlier, so the comment is stale.
I'll drop the kdump mention in a v2.

Thanks for looking at this.

Yuanhe