linux-kernel - Re: [PATCH] mm/memory_hotplug: return zero from do_migrate

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Message-Id: <20230215180316.75431-1-sj@kernel.org>
Date:   Wed, 15 Feb 2023 18:03:16 +0000
From:   SeongJae Park <sj@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     SeongJae Park <sj@...nel.org>, akpm@...ux-foundation.org,
        osalvador@...e.de, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/memory_hotplug: return zero from do_migrate_range() for only success

On Wed, 15 Feb 2023 14:16:05 +0100 David Hildenbrand <david@...hat.com> wrote:

> On 14.02.23 23:32, SeongJae Park wrote:
> > do_migrate_range() returns migrate_pages() return value, which zero
> > means perfect success, in usual cases.  If all pages are failed to be
> > isolated, however, it returns isolate_{lru,movalbe}_page() return
> > values, or zero if all pfn were invalid, were hugetlb or hwpoisoned.  So
> > do_migrate_range() returning zero means either perfect success, or
> > special cases of isolation total failure.
> > 
> > Actually, the return value is not checked by any caller, so it might be
> > better to simply make it a void function.  However, there is a TODO for
> > checking the return value.
> 
> I'd prefer to not add more dead code ;) Let's not return an error instead.

Makes sense, I will send next spin soon.

> 
> It's still unclear which kind of fatal migration issues we actually care 
> about and how to really detect them.

What do you think about treating the isolation/migration rate limit
(migrate_rs) hit in do_migrate_range() as fatal?  It warns for the event
already, so definitely a bad sign.

If that's not that bad enough to be treated as fatal, I think we could have yet
another rate limit to be considered fatal.


Thanks,
SJ

> 
> -- 
> Thanks,
> 
> David / dhildenb