linux-kernel - Re: [PATCH v2 0/5] kdump: crashkernel reservation from CMA

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Message-ID: <aDgQ0lbt1h5v0lgE@tiehlicka>
Date: Thu, 29 May 2025 09:46:26 +0200
From: Michal Hocko <mhocko@...e.com>
To: David Hildenbrand <david@...hat.com>
Cc: Baoquan He <bhe@...hat.com>, Donald Dutile <ddutile@...hat.com>,
	Jiri Bohac <jbohac@...e.cz>, Vivek Goyal <vgoyal@...hat.com>,
	Dave Young <dyoung@...hat.com>, kexec@...ts.infradead.org,
	Philipp Rudo <prudo@...hat.com>, Pingfan Liu <piliu@...hat.com>,
	Tao Liu <ltao@...hat.com>, linux-kernel@...r.kernel.org,
	David Hildenbrand <dhildenb@...hat.com>
Subject: Re: [PATCH v2 0/5] kdump: crashkernel reservation from CMA

On Wed 28-05-25 23:01:04, David Hildenbrand wrote:
[...]
> I think we just have to be careful to document it properly -- especially the
> shortcomings and that this feature might become a problem in the future.
> Movable user-space page tables getting placed on CMA memory would probably
> not be a problem if we don't care about ... user-space data either way.

I think makedumpfile could refuse to capture a dump if userspace memory
is requested to enforce this.

> The whole "Direct I/O takes max 1s" part is a bit shaky. Maybe it could be
> configurable how long to wait? 10s is certainly "safer".

Quite honestly we will never know and rather than making this
configurable I would go with reasonably large. Couple of seconds
certainly do not matter for the kdump situations but I would go as far
as minutes.

-- 
Michal Hocko
SUSE Labs