Re: [PATCH v3] mm/gup: stop leaking pinned pages in low memory conditions

[Alistair Popple <apopple@nvidia.com>]

John Hubbard <jhubbard@nvidia.com> writes:

> On 10/20/24 4:26 PM, Alistair Popple wrote:
>> John Hubbard <jhubbard@nvidia.com> writes:
>> [...]
>>> @@ -2437,8 +2440,10 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
>>>   	long i, ret;
>>>     	folios = kmalloc_array(nr_pages, sizeof(*folios), GFP_KERNEL);
>>> -	if (!folios)
>>> +	if (!folios) {
>>> +		unpin_user_pages(pages, nr_pages);
>> ie. Doesn't this unpinning need to happen in
>> check_and_migrate_movable_folios()?
>
> It already does.
>
> check_and_migrate_movable_folios() calls
> migrate_longterm_unpinnable_folios(), which unpins if errors occur.

Right you are.

Reviewed-by: Alistair Popple <apopple@nvidia.com>

As an aside for future clean-ups we could probably get something nicer
if we reversed the process of pin/migrate to migrate/pin. In other words
if FOLL_LONGERM try and migrate the entire range first out of
ZONE_MOVABLE first. Migration invovles walking page tables and getting a
reference on the pages anyway, so if it turns out there is nothing to
migrate you haven't lost anything performance wise.

> thanks,