linux-kernel - Re: [PATCH v8 01/17] memblock: add MEMBLOCK_RSRV

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Message-ID: <2ege2jfbevtunhxsnutbzde7cqwgu5qbj4bbuw2umw7ke7ogcn@5wtskk4exzsi>
Date: Tue, 14 Oct 2025 01:34:07 -0700
From: Breno Leitao <leitao@...ian.org>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: Changyuan Lyu <changyuanl@...gle.com>, rppt@...nel.org, 
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Subject: Re: [PATCH v8 01/17] memblock: add MEMBLOCK_RSRV_KERN flag

Hello Pratyush,

On Mon, Oct 13, 2025 at 06:40:09PM +0200, Pratyush Yadav wrote:
> On Mon, Oct 13 2025, Pratyush Yadav wrote:
> >
> > I suppose this would be useful. I think enabling memblock debug prints
> > would also be helpful (using the "memblock=debug" commandline parameter)
> > if it doesn't impact your production environment too much.
> 
> Actually, I think "memblock=debug" is going to be the more useful thing
> since it would also show what function allocated the overlapping range
> and the flags it was allocated with.
> 
> On my qemu VM with KVM, this results in around 70 prints from memblock.
> So it adds a bit of extra prints but nothing that should be too
> disrupting I think. Plus, only at boot so the worst thing you get is
> slightly slower boot times.

Unfortunately this issue is happening on production systems, and I don't
have an easy way to reproduce it _yet_.

At the same time, "memblock=debug" has two problems:

 1) It slows the boot time as you suggested. Boot time at large
    environments is SUPER critical and time sensitive. It is a bit
    weird, but it is common for machines in production to kexec
    _thousands_ of times, and kexecing is considered downtime.

    This would be useful if I find some hosts getting this issue, and
    then I can easily enable the extra information to collect what
    I need, but, this didn't pan out because the hosts I got
    `memblock=debug` didn't collaborate.

 2) "memblock=debug" is verbose for all cases, which also not necessary
    the desired behaviour. I am more interested in only being verbose
    when there is a known problem.

That said, my suggestion is to only dump extra information when something goes
wrong, not affecting the boot time neither boot verbosity.