On Wed 10-03-21 10:56:08, Mike Kravetz wrote:
> On 3/10/21 7:19 AM, Michal Hocko wrote:
> > On Mon 08-03-21 18:28:02, Muchun Song wrote:
> > [...]
> >> @@ -1447,7 +1486,7 @@ void free_huge_page(struct page *page)
> >> /*
> >> * Defer freeing if in non-task context to avoid hugetlb_lock deadlock.
> >> */
> >> - if (!in_task()) {
> >> + if (in_atomic()) {
> >
> > As I've said elsewhere in_atomic doesn't work for CONFIG_PREEMPT_COUNT=n.
> > We need this change for other reasons and so it would be better to pull
> > it out into a separate patch which also makes HUGETLB depend on
> > PREEMPT_COUNT.
>
> Yes, the issue of calling put_page for hugetlb pages from any context
> still needs work. IMO, that is outside the scope of this series. We
> already have code in this path which blocks/sleeps.
>
> Making HUGETLB depend on PREEMPT_COUNT is too restrictive. IIUC,
> PREEMPT_COUNT will only be enabled if we enable:
> PREEMPT "Preemptible Kernel (Low-Latency Desktop)"
> PREEMPT_RT "Fully Preemptible Kernel (Real-Time)"
> or, other 'debug' options. These are not enabled in 'more common'
> kernels. Of course, we do not want to disable HUGETLB in common
> configurations.
I haven't tried that but PREEMPT_COUNT should be selectable even without
any change to the preemption model (e.g. !PREEMPT).
--
Michal Hocko
SUSE Labs
