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

[Kefeng Wang]

On 2024/7/31 16:56, Baolin Wang wrote:
> 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.

Maybe drop unsigned long orders too?

diff --git a/mm/shmem.c b/mm/shmem.c
index 6af95f595d6f..8485eb6f2ec4 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1638,11 +1638,6 @@ 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 ? vma->vm_flags : 0;
-       /*
-        * Check all the (large) orders below HPAGE_PMD_ORDER + 1 that
-        * are enabled for this vma.
-        */
-       unsigned long orders = BIT(PMD_ORDER + 1) - 1;
        bool global_huge;
        loff_t i_size;
        int order;
@@ -1698,7 +1693,7 @@ unsigned long shmem_allowable_huge_orders(struct 
inode *inode,
        if (global_huge)
                mask |= READ_ONCE(huge_shmem_orders_inherit);

-       return orders & mask;
+       return THP_ORDERS_ALL_FILE_DEFAULT & mask;
 }

> 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;