linux-kernel - Re: [PATCH 7/7] mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case

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Date:   Mon, 10 Feb 2020 14:08:04 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     Wei Yang <richardw.yang@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, dan.j.williams@...el.com,
        david@...hat.com
Subject: Re: [PATCH 7/7] mm/hotplug: fix hot remove failure in
 SPARSEMEM|!VMEMMAP case

On Mon, Feb 10, 2020 at 11:41:05AM +0800, Baoquan He wrote:
>On 02/10/20 at 07:52am, Wei Yang wrote:
>> >---
>> > mm/sparse.c | 4 +++-
>> > 1 file changed, 3 insertions(+), 1 deletion(-)
>> >
>> >diff --git a/mm/sparse.c b/mm/sparse.c
>> >index 623755e88255..345d065ef6ce 100644
>> >--- a/mm/sparse.c
>> >+++ b/mm/sparse.c
>> >@@ -854,13 +854,15 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
>> > 			ms->usage = NULL;
>> > 		}
>> > 		memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
>> >-		ms->section_mem_map = (unsigned long)NULL;
>> > 	}
>> > 
>> > 	if (section_is_early && memmap)
>> > 		free_map_bootmem(memmap);
>> > 	else
>> > 		depopulate_section_memmap(pfn, nr_pages, altmap);
>> 
>> The crash happens in depopulate_section_memmap() when trying to get memmap by
>> pfn_to_page(). Can we pass memmap directly?
>
>Yes, that's also a good idea. While it needs to add a parameter for
>depopulate_section_memmap(), the parameter is useless for VMEMMAP
>though, I personally prefer the current fix which is a little simpler.
>

Not a new parameter, but replace pfn with memmap.

Not sure why the parameter is useless for VMEMMAP? memmap will be assigned to
start and finally pass to vmemmap_free().

>Anyway, both is fine to me, I can update if you think passing memmap is
>better.
>
>> 
>> >+
>> >+	if(!rc)
>> >+		ms->section_mem_map = (unsigned long)NULL;
>> > }
>> > 
>> > static struct page * __meminit section_activate(int nid, unsigned long pfn,
>> >-- 
>> >2.17.2
>> 
>> -- 
>> Wei Yang
>> Help you, Help me
>> 

-- 
Wei Yang
Help you, Help me