linux-kernel - Re: [PATCH v2 1/2] mm/memory_hotplug: return nothing from do_migrate

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Date:   Thu, 16 Feb 2023 16:55:12 +0000
From:   SeongJae Park <sj@...nel.org>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     SeongJae Park <sj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mm/memory_hotplug: return nothing from do_migrate_range()

Hi Baolin,

On Thu, 16 Feb 2023 18:53:34 +0800 Baolin Wang <baolin.wang@...ux.alibaba.com> wrote:

> 
> 
> On 2/16/2023 7:02 AM, SeongJae Park wrote:
> > Return value mechanism of do_migrate_range() is not very simple, while
> > no caller of the function checks the return value.  Make the function
> > return nothing to be more simple.
> > 
> > Suggested-by: David Hildenbrand <david@...hat.com>
> > Signed-off-by: SeongJae Park <sj@...nel.org>
> > ---
> >   mm/memory_hotplug.c | 5 +----
> >   1 file changed, 1 insertion(+), 4 deletions(-)
> > 
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index bcb0dc41c2f2..6c615ba1a5c7 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -1620,8 +1620,7 @@ static int scan_movable_pages(unsigned long start, unsigned long end,
> >   	return 0;
> >   }
> >   
> > -static int
> > -do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> > +static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> >   {
> >   	unsigned long pfn;
> >   	struct page *page, *head;
> > @@ -1721,8 +1720,6 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
> >   			putback_movable_pages(&source);
> >   		}
> >   	}
> > -
> > -	return ret;
> 
> Nit: while we are at it, can we also remove the "TODO" comment in 
> offline_pages()?
> 
> ret = scan_movable_pages(pfn, end_pfn, &pfn);
> if (!ret) {
> 	/*
> 	 * TODO: fatal migration failures should bail
> 	 * out
> 	 */
> 	do_migrate_range(pfn, end_pfn);
> }
> 
> With David's comments:
> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>

As David mentioned we're just still unclear what issues are fatal[1], I was
thinking we didn't forgive the future work, so left the comment.  If anyone has
different opinion or I'm getting something wrong, please let me know.

[1] https://lore.kernel.org/linux-mm/388b9a93-423f-33f8-0495-2a4a290fd1aa@redhat.com/


Thanks,
SJ