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

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Message-ID: <cacd14a9-01fc-4844-9ac6-2e797af13c36@gmail.com>
Date: Mon, 24 Jun 2024 20:26:39 +0300
From: Usama Arif <usamaarif642@...il.com>
To: Yosry Ahmed <yosryahmed@...gle.com>, Hugh Dickins <hughd@...gle.com>
Cc: 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, "Vlastimil Babka (SUSE)" <vbabka@...nel.org>,
 Yury Norov <yury.norov@...il.com>,
 Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [linux-next:master] [mm] 0fa2857d23:
 WARNING:at_mm/page_alloc.c:#__alloc_pages_noprof


On 24/06/2024 19:56, Yosry Ahmed wrote:
> [..]
>>>> -       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);
> You can do something similar to bitmap_zalloc() and use:
>
> kvmalloc_array(BITS_TO_LONGS(nbits), sizeof(unsigned long), GFP_KERNEL
> | __GFP_ZERO)
>
> I don't see a kvzalloc_array() variant to use directly, but it should
> be trivial to add it. I can see other users of kvmalloc_array() that
> pass in __GFP_ZERO (e.g. fs/ntfs3/bitmap.c).
>
> , or you could take it a step further and add bitmap_kvzalloc(),
> assuming the maintainers are open to that.

Thanks! bitmap_kvzalloc makes most sense to me. It doesnt make sense 
that bitmap should only be limited to MAX_PAGE_ORDER size. I can add 
this patch below at the start of the series and use it in the patch for 
zeropage swap optimization.


     bitmap: add support for virtually contiguous bitmap

     The current bitmap_zalloc API limits the allocation to MAX_PAGE_ORDER,
     which prevents larger order bitmap allocations. Introduce
     bitmap_kvzalloc that will allow larger allocations of bitmap.
     kvmalloc_array still attempts to allocate physically contiguous memory,
     but upon failure, falls back to non-contiguous (vmalloc) allocation.

     Suggested-by: Yosry Ahmed <yosryahmed@...gle.com>
     Signed-off-by: Usama Arif <usamaarif642@...il.com>

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 8c4768c44a01..881c2ff2e834 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -131,9 +131,11 @@ struct device;
   */
  unsigned long *bitmap_alloc(unsigned int nbits, gfp_t flags);
  unsigned long *bitmap_zalloc(unsigned int nbits, gfp_t flags);
+unsigned long *bitmap_kvzalloc(unsigned int nbits, gfp_t flags);
  unsigned long *bitmap_alloc_node(unsigned int nbits, gfp_t flags, int 
node);
  unsigned long *bitmap_zalloc_node(unsigned int nbits, gfp_t flags, int 
node);
  void bitmap_free(const unsigned long *bitmap);
+void bitmap_kvfree(const unsigned long *bitmap);

  DEFINE_FREE(bitmap, unsigned long *, if (_T) bitmap_free(_T))

diff --git a/lib/bitmap.c b/lib/bitmap.c
index b97692854966..eabbfb85fb45 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -727,6 +727,13 @@ unsigned long *bitmap_zalloc(unsigned int nbits, 
gfp_t flags)
  }
  EXPORT_SYMBOL(bitmap_zalloc);

+unsigned long *bitmap_kvzalloc(unsigned int nbits, gfp_t flags)
+{
+       return kvmalloc_array(BITS_TO_LONGS(nbits), sizeof(unsigned long),
+                             flags | __GFP_ZERO);
+}
+EXPORT_SYMBOL(bitmap_zalloc);
+
  unsigned long *bitmap_alloc_node(unsigned int nbits, gfp_t flags, int 
node)
  {
         return kmalloc_array_node(BITS_TO_LONGS(nbits), sizeof(unsigned 
long),
@@ -746,6 +753,12 @@ void bitmap_free(const unsigned long *bitmap)
  }
  EXPORT_SYMBOL(bitmap_free);

+void bitmap_kvfree(const unsigned long *bitmap)
+{
+       kvfree(bitmap);
+}
+EXPORT_SYMBOL(bitmap_kvfree);
+
  static void devm_bitmap_free(void *data)
  {
         unsigned long *bitmap = data;


>
> The main reason I want to avoid doing the multiplication inline is
> because kvmalloc_array() has a check_mul_overflow() check, and I
> assume it must have been added for a reason.