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Message-ID: <db464483-5aa1-499d-9e66-ac30541499f9@redhat.com>
Date: Wed, 31 Jul 2024 11:18:53 +0200
From: David Hildenbrand <david@...hat.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
hughd@...gle.com
Cc: willy@...radead.org, 21cnbao@...il.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 2/2] mm: shmem: fix incorrect aligned index when checking
conflicts
On 31.07.24 07:46, Baolin Wang wrote:
> In the shmem_suitable_orders() function, xa_find() is used to check for
> conflicts in the pagecache to select suitable huge orders. However, when
> checking each huge order in every loop, the aligned index is calculated
> from the previous iteration, which may cause suitable huge orders to be
> missed.
>
> We should use the original index each time in the loop to calculate a
> new aligned index for checking conflicts to avoid this issue.
>
> Fixes: e7a2ab7b3bb5 ("mm: shmem: add mTHP support for anonymous shmem")
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
> mm/shmem.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index a4332a97558c..6e9836b1bd1d 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1686,6 +1686,7 @@ static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault
> unsigned long orders)
> {
> struct vm_area_struct *vma = vmf->vma;
> + pgoff_t aligned_index;
> unsigned long pages;
> int order;
>
> @@ -1697,9 +1698,9 @@ static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault
> order = highest_order(orders);
> while (orders) {
> pages = 1UL << order;
> - index = round_down(index, pages);
> - if (!xa_find(&mapping->i_pages, &index,
> - index + pages - 1, XA_PRESENT))
> + aligned_index = round_down(index, pages);
> + if (!xa_find(&mapping->i_pages, &aligned_index,
> + aligned_index + pages - 1, XA_PRESENT))
> break;
> order = next_order(&orders, order);
> }
Acked-by: David Hildenbrand <david@...hat.com>
--
Cheers,
David / dhildenb
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