linux-kernel - Re: [linux-next:master] [mm] 0fa2857d23: WARNING:at_mm/page_alloc.c:#__alloc_pages

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Message-ID: <5b3e732c-d23d-41ef-ae5c-947fa3e866ab@gmail.com>
Date: Mon, 24 Jun 2024 18:39:01 +0300
From: Usama Arif <usamaarif642@...il.com>
To: Hugh Dickins <hughd@...gle.com>
Cc: Yosry Ahmed <yosryahmed@...gle.com>,
 kernel test robot <oliver.sang@...el.com>, oe-lkp@...ts.linux.dev,
 lkp@...el.com, Linux Memory Management List <linux-mm@...ck.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Chengming Zhou <chengming.zhou@...ux.dev>, Nhat Pham <nphamcs@...il.com>,
 David Hildenbrand <david@...hat.com>, "Huang, Ying" <ying.huang@...el.com>,
 Johannes Weiner <hannes@...xchg.org>, Matthew Wilcox <willy@...radead.org>,
 Shakeel Butt <shakeel.butt@...ux.dev>, Andi Kleen <ak@...ux.intel.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [linux-next:master] [mm] 0fa2857d23:
 WARNING:at_mm/page_alloc.c:#__alloc_pages_noprof


On 24/06/2024 18:26, Hugh Dickins wrote:
> On Mon, 24 Jun 2024, Usama Arif wrote:
>> On 24/06/2024 15:05, Yosry Ahmed wrote:
>>> On Mon, Jun 24, 2024 at 1:49 AM kernel test robot <oliver.sang@...el.com>
>>> wrote:
>>>>
>>>> Hello,
>>>>
>>>> kernel test robot noticed
>>>> "WARNING:at_mm/page_alloc.c:#__alloc_pages_noprof" on:
>>>>
>>>> commit: 0fa2857d23aa170e5e28d13c467b303b0065aad8 ("mm: store zero pages to
>>>> be swapped out in a bitmap")
>>>> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
>>> This is coming from WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp), and
>>> is triggered by the new bitmap_zalloc() call in the swapon path. For a
>>> sufficiently large swapfile, bitmap_zalloc() (which uses kmalloc()
>>> under the hood) cannot be used to allocate the bitmap.
>>>
>>> Usama, I think we want to use a variant of kvmalloc() here.
> Yes, I hit the same problem with swapon in my testing,
> and had been intending to send a patch.
>
>> Yes, just testing with below diff now. The patch is not in mm-stable yet, so
>> will just send another revision with below diff included. Thanks!
>>
>>
>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>> index 0b8270359bcf..2263f71baa31 100644
>> --- a/mm/swapfile.c
>> +++ b/mm/swapfile.c
>> @@ -2643,7 +2643,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *,
>> specialfile)
>>          free_percpu(p->cluster_next_cpu);
>>          p->cluster_next_cpu = NULL;
>>          vfree(swap_map);
>> -       bitmap_free(p->zeromap);
>> +       kvfree(p->zeromap);
> Yes.
>
>>          kvfree(cluster_info);
>>          /* Destroy swap account information */
>>          swap_cgroup_swapoff(p->type);
>> @@ -3170,7 +3170,7 @@ SYSCALL_DEFINE2(swapon, const char __user *,
>> specialfile, int, swap_flags)
>>                  goto bad_swap_unlock_inode;
>>          }
>>
>> -       p->zeromap = bitmap_zalloc(maxpages, GFP_KERNEL);
>> +       p->zeromap = kvzalloc(DIV_ROUND_UP(maxpages, 8), GFP_KERNEL);
> No, 8 is not right for 32-bit kernels. I think you want
> 	p->zeromap = kvzalloc(BITS_TO_LONGS(maxpages), GFP_KERNEL);
> but please check it carefully, I'm easily confused by such conversions.
>
> Hugh

Ah yes, didnt take into account 32-bit kernel. I think its supposed to be

  p->zeromap = kvzalloc(BITS_TO_LONGS(maxpages) * sizeof(unsigned long), 
GFP_KERNEL);

if using BITS_TO_LONGS.

Will wait sometime incase there are more comments and will send out 
another version.

Thanks!

>>          if (!p->zeromap) {
>>                  error = -ENOMEM;
>>                  goto bad_swap_unlock_inode;