On Thu 18-02-21 11:20:51, Muchun Song wrote:

On Thu, Feb 18, 2021 at 9:00 AM Mike Kravetz [off-list ref] wrote:

quoted

On 2/17/21 12:13 AM, Michal Hocko wrote:

quoted

On Tue 16-02-21 11:44:34, Mike Kravetz wrote:
[...]

quoted

If we are not going to do the allocations under the lock, then we will need
to either preallocate or take the workqueue approach.

We can still drop the lock temporarily right? As we already do before
calling destroy_compound_gigantic_page...

Yes we can.  I forgot about that.

Actually, very little of what update_and_free_page does needs to be done
under the lock.  Perhaps, just decrementing the global count and clearing
the destructor so PageHuge() is no longer true.

Right. I have another question about using GFP flags. Michal
suggested using GFP_KERNEL instead of GFP_ATOMIC to
save reserve memory. From your last email, you suggested
using non-blocking allocation GFP flags (perhaps GFP_NOWAIT).

Hi Mike and Michal,

What is the consensus we finally reached? Thanks.

If the lock can be dropped and you make sure the final put on page is
not called from an atomic context then use (for starter)
GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE. I have intentionaly dropped
__GFP_NOWARN because likely want to hear about the failure so that we
can evaluate how often this happens.

This would be my recommendation.
-- 
Michal Hocko
SUSE Labs