linux-kernel - Re: [PATCH 1/2] mm: shmem: avoid allocating huge pages larger than MAX_PAGECACHE

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Message-ID: <CAGsJ_4xmHY06VAKzXxCFcovPkrR0WOR28jXbaeD5VyUBHWzn_w@mail.gmail.com>
Date: Wed, 31 Jul 2024 14:18:02 +0800
From: Barry Song <21cnbao@...il.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: akpm@...ux-foundation.org, hughd@...gle.com, willy@...radead.org, 
	david@...hat.com, ryan.roberts@....com, ziy@...dia.com, gshan@...hat.com, 
	ioworker0@...il.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm: shmem: avoid allocating huge pages larger than
 MAX_PAGECACHE_ORDER for shmem

On Wed, Jul 31, 2024 at 1:46 PM Baolin Wang
<baolin.wang@...ux.alibaba.com> 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@...ux.alibaba.com>

Reviewed-by: Barry Song <baohua@...nel.org>

> ---
>  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?

>          */
> -       unsigned long orders = BIT(PMD_ORDER + 1) - 1;
> +       unsigned long orders = THP_ORDERS_ALL_FILE_DEFAULT;
>         loff_t i_size;
>         int order;
>
> --
> 2.39.3
>

Thanks
Barry