On Mon, Jun 22, 2020 at 11:51:34AM +0200, David Hildenbrand wrote:
On 22.06.20 11:22, Wei Yang wrote:
On Mon, Jun 22, 2020 at 10:43:11AM +0200, David Hildenbrand wrote:
On 22.06.20 10:26, Wei Yang wrote:
On Fri, Jun 19, 2020 at 02:59:20PM +0200, David Hildenbrand wrote:
Especially with memory hotplug, we can have offline sections (with a garbage memmap) and overlapping zones. We have to make sure to only touch initialized memmaps (online sections managed by the buddy) and that the zone matches, to not move pages between zones.
To test if this can actually happen, I added a simple BUG_ON(page_zone(page_i) != page_zone(page_j)); right before the swap. When hotplugging a 256M DIMM to a 4G x86-64 VM and onlining the first memory block "online_movable" and the second memory block "online_kernel", it will trigger the BUG, as both zones (NORMAL and MOVABLE) overlap.
This might result in all kinds of weird situations (e.g., double allocations, list corruptions, unmovable allocations ending up in the movable zone).
Fixes: e900a918b098 ("mm: shuffle initial free memory to improve memory-side-cache utilization") Acked-by: Michal Hocko mhocko@suse.com Cc: stable@vger.kernel.org # v5.2+ Cc: Andrew Morton akpm@linux-foundation.org Cc: Johannes Weiner hannes@cmpxchg.org Cc: Michal Hocko mhocko@suse.com Cc: Minchan Kim minchan@kernel.org Cc: Huang Ying ying.huang@intel.com Cc: Wei Yang richard.weiyang@gmail.com Cc: Mel Gorman mgorman@techsingularity.net Signed-off-by: David Hildenbrand david@redhat.com
mm/shuffle.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-)
diff --git a/mm/shuffle.c b/mm/shuffle.c index 44406d9977c77..dd13ab851b3ee 100644 --- a/mm/shuffle.c +++ b/mm/shuffle.c @@ -58,25 +58,25 @@ module_param_call(shuffle, shuffle_store, shuffle_show, &shuffle_param, 0400);
- For two pages to be swapped in the shuffle, they must be free (on a
- 'free_area' lru), have the same order, and have the same migratetype.
*/ -static struct page * __meminit shuffle_valid_page(unsigned long pfn, int order) +static struct page * __meminit shuffle_valid_page(struct zone *zone,
unsigned long pfn, int order){
- struct page *page;
- struct page *page = pfn_to_online_page(pfn);
Hi, David and Dan,
One thing I want to confirm here is we won't have partially online section, right? We can add a sub-section to system, but we won't manage it by buddy.
Hi,
there is still a BUG with sub-section hot-add (devmem), which broke pfn_to_online_page() in corner cases (especially, see the description in include/linux/mmzone.h). We can have a boot-memory section partially populated and marked online. Then, we can hot-add devmem, marking the remaining pfns valid - and as the section is maked online, also as online.
Oh, yes, I see this description.
This means we could have section marked as online, but with a sub-section even not added.
While the good news is even the sub-section is not added, but its memmap is populated for an early section. So the page returned from pfn_to_online_page() is a valid one.
But what would happen, if the sub-section is removed after added? Would section_deactivate() release related memmap to this "struct page"?
If devmem is removed, the memmap will be freed and the sub-sections are marked as non-present. So this works as expected.
Sorry, I may not catch your point. If my understanding is correct, the above behavior happens in function section_deactivate().
Let me draw my understanding of function section_deactivate():
section_deactivate(pfn, nr_pages) clear_subsection_map(pfn, nr_pages) depopulate_section_memmap(pfn, nr_pages)
Since we just remove a sub-section, I skipped some un-related codes. These two functions would:
* clear bitmap in ms->usage->subsection_map * free memmap for the sub-section
While since the section is not empty, ms->section_mem_map is not set no null.
Per my understanding, the section present state is set in ms->section_mem_map with SECTION_MARKED_PRESENT. It looks we don't clear it when just remote a sub-section.
Do I miss something?
-- Thanks,
David / dhildenb