linux-kernel - Re: [RFC PATCH v2 10/16] mm,hwpoison: Rework soft offline for free pages

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Message-ID: <20191022083505.GA19708@linux>
Date:   Tue, 22 Oct 2019 10:35:17 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     n-horiguchi@...jp.nec.com, mike.kravetz@...cle.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 10/16] mm,hwpoison: Rework soft offline for free
 pages

On Tue, Oct 22, 2019 at 10:26:11AM +0200, Michal Hocko wrote:
> On Tue 22-10-19 09:46:20, Oscar Salvador wrote:
> [...]
> > So, opposite to hard-offline, in soft-offline we do not fiddle with pages
> > unless we are sure the page is not reachable anymore by any means.
> 
> I have to say I do not follow. Is there any _real_ reason for
> soft-offline to behave differenttly from MCE (hard-offline)?

Yes.
Do not take it as 100% true as I read that in some code/Documentation
a while ago.

But I think that it boils down to:

soft-offline: "We have seen some erros in the underlying page, but
               it is still usable, so we have a chance to keep the
               the contents (via migration)"
hard-offline: "The underlying page is dead, we cannot trust it, so
               we shut it down, killing whoever is holding it
               along the way".

Am I wrong Naoya?

-- 
Oscar Salvador
SUSE L3