On 2/28/25 10:20, Brendan Jackman wrote:
> On Thu, Feb 27, 2025 at 02:33:02PM -0800, Andrew Morton wrote:
>> On Thu, 27 Feb 2025 16:15:47 +0000 Brendan Jackman <jackmanb@xxxxxxxxxx> wrote:
>>
>> > Since the migratetype hygiene patches [0], the locking here is
>> > a bit more formalised, so write it down with an assert.
>> >
>> > ...
>> >
>> > --- a/mm/page_alloc.c
>> > +++ b/mm/page_alloc.c
>> > @@ -417,6 +417,10 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags,
>> >
>> > void set_pageblock_migratetype(struct page *page, int migratetype)
>> > {
>> > + lockdep_assert_once(system_state == SYSTEM_BOOTING ||
>> > + in_mem_hotplug() ||
>> > + lockdep_is_held(&page_zone(page)->lock));
>> > +
>> > if (unlikely(page_group_by_mobility_disabled &&
>> > migratetype < MIGRATE_PCPTYPES))
>> > migratetype = MIGRATE_UNMOVABLE;
>> >
>>
>> We could add such assertions all over the place. Why this place in
>> particular?
>
> For the other stuff, it's pretty obvious that it would be protected by
> the zone lock (or, I don't know about it!). But it didn't seem totally
> self-evident to me that it should protect the pageblock type. So it
> seems particularly helpful to have it written in the code.
I guess that's a good addition to the changelog.
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
>
> I may be heavily biased about this though, because of the code I'm
> working on for [0]. I use the pageblock type to remember whether it's
> mapped in the ASI restricted address space.
>
> [0] https://lore.kernel.org/linux-mm/CA+i-1C1gOBLxRxE5YFGzeayYWBYyE_X6oH4D=9eVePt4=ehTig@xxxxxxxxxxxxxx/T/
>
