On Thu, Apr 18, 2024 at 12:46:39AM +0100, Matthew Wilcox wrote:
> On Wed, Apr 17, 2024 at 05:18:34PM -0400, Peter Xu wrote:
> > Current mm-unstable will hit this when running test_hugetlb_memcg. This
> > fixes the crash for me.
[1]
> >
> > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> > ---
> > mm/memcontrol.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 1840ba4c355d..7703ced535a3 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -7529,6 +7529,7 @@ static void uncharge_folio(struct folio *folio, struct uncharge_gather *ug)
> >
> > VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
> > VM_BUG_ON_FOLIO(folio_order(folio) > 1 &&
> > + !folio_test_hugetlb(folio) &&
> > !list_empty(&folio->_deferred_list), folio);
>
> Hum. I thought we didn't get here for hugetlb folios. What
> stacktrace did you get?
A normal hugetlb free path iirc. You can try the test case, I mentioned
the reproducer [1] above. It crashes constantly.
>
> I'm basing it on comments like this:
>
> /* hugetlb has its own memcg */
> if (folio_test_hugetlb(folio)) {
> if (lruvec) {
> unlock_page_lruvec_irqrestore(lruvec, flags);
> lruvec = NULL;
> }
> free_huge_folio(folio);
> continue;
> }
Hugetlb does have its own memcg but I guess now it's even more than that,
see the patch merged months ago:
https://lore.kernel.org/all/20231006184629.155543-4-nphamcs@xxxxxxxxx/
Especially:
@@ -1902,6 +1902,7 @@ void free_huge_folio(struct folio *folio)
pages_per_huge_page(h), folio);
hugetlb_cgroup_uncharge_folio_rsvd(hstate_index(h),
pages_per_huge_page(h), folio);
+ mem_cgroup_uncharge(folio);
if (restore_reserve)
h->resv_huge_pages++;
The comment above looks a bit confusing to me, as memcg is not the only
thing special for hugetlb pages. Explicitly mentioning it there made me
feel like hugetlb can be freed like a normal compound page if memcg is not
a problem, but looks like not yet?
--
Peter Xu
