Re: [PATCH 1/2] mm: shmem: avoid allocating huge pages larger than MAX_PAGECACHE_ORDER for shmem

[Baolin Wang]

On 2024/7/31 14:18, Barry Song wrote:
> On Wed, Jul 31, 2024 at 1:46 PM Baolin Wang
> <baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
> > Similar to commit d659b715e94ac ("mm/huge_memory: avoid PMD-size page cache
> > if needed"), ARM64 can support 512MB PMD-sized THP when the base page size is
> > 64KB, which is larger than the maximum supported page cache size MAX_PAGECACHE_ORDER.
> > This is not expected. To fix this issue, use THP_ORDERS_ALL_FILE_DEFAULT for
> > shmem to filter allowable huge orders.
> >
> > Fixes: e7a2ab7b3bb5 ("mm: shmem: add mTHP support for anonymous shmem")
> > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>
> Reviewed-by: Barry Song <baohua@xxxxxxxxxx>

Thanks for reviewing.

> > ---
> >   mm/shmem.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/shmem.c b/mm/shmem.c
> > index 2faa9daaf54b..a4332a97558c 100644
> > --- a/mm/shmem.c
> > +++ b/mm/shmem.c
> > @@ -1630,10 +1630,10 @@ unsigned long shmem_allowable_huge_orders(struct inode *inode,
> >          unsigned long within_size_orders = READ_ONCE(huge_shmem_orders_within_size);
> >          unsigned long vm_flags = vma->vm_flags;
> >          /*
> > -        * Check all the (large) orders below HPAGE_PMD_ORDER + 1 that
> > +        * Check all the (large) orders below MAX_PAGECACHE_ORDER + 1 that
> >           * are enabled for this vma.
>
> Nit:
> THP_ORDERS_ALL_FILE_DEFAULT should be self-explanatory enough.
> I feel we don't need this comment?

Sure.

Andrew, please help to squash the following changes into this patch. Thanks.

diff --git a/mm/shmem.c b/mm/shmem.c
index 6e9836b1bd1d..432faec21547 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1629,10 +1629,6 @@ unsigned long shmem_allowable_huge_orders(struct 
inode *inode,
        unsigned long mask = READ_ONCE(huge_shmem_orders_always);
        unsigned long within_size_orders = 
READ_ONCE(huge_shmem_orders_within_size);
        unsigned long vm_flags = vma->vm_flags;
-       /*
-        * Check all the (large) orders below MAX_PAGECACHE_ORDER + 1 that
-        * are enabled for this vma.
-        */
        unsigned long orders = THP_ORDERS_ALL_FILE_DEFAULT;
        loff_t i_size;
        int order;