Re: [PATCH RFC] mm: allow __GFP_NOFAIL allocation up to BLK_MAX_BLOCK_SIZE to support LBS

[Baokun Li <libaokun1@huawei.com>]

Hi,

Sorry for the late reply, I was traveling of office.

Thanks to Matthew for helping with the explanation.

On 2025-11-01 00:55, Matthew Wilcox wrote:
> On Fri, Oct 31, 2025 at 09:46:17AM -0700, Shakeel Butt wrote:
>> Now for the interface to allow NOFS+NOFAIL+higher_order, I think a new
>> (FS specific) gfp is fine but will require some maintenance to avoid
>> abuse.
> I don't think a new GFP flag is the answer.  GFP_TRUST_ME_BRO just
> doesn't feel right.

Agreed. If we add a new GFP flag, it will be hard to prevent its misuse,
and __GFP_NOFAIL is a good example of this; we simply have no way to
monitor all callers.

>> I am more interested in how to codify "you can reclaim one I've already
>> allocated". I have a different scenario where network stack keep
>> stealing memory from direct reclaimers and keeping them in reclaim for
>> long time. If we have some mechanism to allow reclaimers to get the
>> memory they have reclaimed (at least for some cases), I think that can
>> be used in both cases.
> The only thing that comes to mind is putting pages freed by reclaim on
> a list in task_struct instead of sending them back to the allocator.
> Then the task can allocate from there and free up anything else it's
> reclaimed at some later point.  I don't think this is a good idea,
> but it's the only idea that comes to mind.

I am not familiar with the MM module, but here is a rough thought:

What about passing the minimum folio order to the allocator?
We could then ensure that pages are freed and allocated using the list
matching that specific order.


Thanks,
Baokun