Re: [PATCH] mm/page_alloc: add one PCP list for THP

[Ge Yang <yangge1116@126.com>]

在 2024/6/20 9:01, Andrew Morton 写道:
> On Wed, 19 Jun 2024 20:54:32 +0800 yangge1116@126.com wrote:
> 
>> From: yangge <yangge1116@126.com>
>>
>> Since commit 5d0a661d808f ("mm/page_alloc: use only one PCP list for
>> THP-sized allocations") no longer differentiates the migration type
>> of pages in THP-sized PCP list, it's possible that non-movable
>> allocation requests may get a CMA page from the list, in some cases,
>> it's not acceptable.
>>
>> If a large number of CMA memory are configured in system (for
>> example, the CMA memory accounts for 50% of the system memory),
>> starting a virtual machine with device passthrough will get stuck.
>> During starting the virtual machine, it will call
>> pin_user_pages_remote(..., FOLL_LONGTERM, ...) to pin memory. Normally
>> if a page is present and in CMA area, pin_user_pages_remote() will
>> migrate the page from CMA area to non-CMA area because of
>> FOLL_LONGTERM flag. But if non-movable allocation requests return
>> CMA memory, migrate_longterm_unpinnable_pages() will migrate a CMA
>> page to another CMA page, which will fail to pass the check in
>> check_and_migrate_movable_pages() and cause migration endless.
>> Call trace:
> 
> Thanks.  I'll add this for testing - please send us a new version which
> addresses Barry's comments.

Ok, thanks.
New version: 
https://lore.kernel.org/lkml/1718845190-4456-1-git-send-email-yangge1116@126.com/