Re: [Xen-devel] [PATCH 03/27] xen/x86: mm: Don't check alloc_boot_pages return

[Julien Grall]

On 22/08/17 12:28, Andre Przywara wrote:

Hi,


Hi Andre,



On 14/08/17 15:23, Julien Grall wrote:

The only way alloc_boot_pages will return 0 is during the error case.


This statement is not true. If alloc_boot_pages() returns, it has
succeeded. Returning 0 is nothing special.


Although, Xen will panic in the error path. So the check in the caller
is pointless.

Looking at the loop, my understanding is it will try to allocate in
smaller chunk if a bigger chunk fail. Given that alloc_boot_pages can
never check, the loop seems unecessary.


Agreed, the algorithm doesn't work with (current) implementation of
alloc_boot_pages(), so the patch is valid.


Signed-off-by: Julien Grall 


Given that you adjust the commit message:

Reviewed-by: Andre Przywara 


The first 3 patches were already committed a few days ago, so we would 
have to stick with the current message.


Cheers,

--
Julien Grall

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Re: [Xen-devel] [PATCH 03/27] xen/x86: mm: Don't check alloc_boot_pages return

[Andre Przywara]

Hi,

On 14/08/17 15:23, Julien Grall wrote:
> The only way alloc_boot_pages will return 0 is during the error case.

This statement is not true. If alloc_boot_pages() returns, it has
succeeded. Returning 0 is nothing special.

> Although, Xen will panic in the error path. So the check in the caller
> is pointless.
> 
> Looking at the loop, my understanding is it will try to allocate in
> smaller chunk if a bigger chunk fail. Given that alloc_boot_pages can
> never check, the loop seems unecessary.

Agreed, the algorithm doesn't work with (current) implementation of
alloc_boot_pages(), so the patch is valid.

> Signed-off-by: Julien Grall 

Given that you adjust the commit message:

Reviewed-by: Andre Przywara 

Cheers,
Andre.

> Cc: Jan Beulich 
> Cc: Andrew Cooper 
> 
> I haven't tested this code, only build test it. I can't see how
> alloc_boot_pages would return 0 other than the error path.
> ---
>  xen/arch/x86/mm.c | 6 +-
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
> index f53ca43554..66e337109d 100644
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -200,11 +200,7 @@ static void __init init_frametable_chunk(void *start, 
> void *end)
>   */
>  while ( step && s + (step << PAGE_SHIFT) > e + (4 << PAGE_SHIFT) )
>  step >>= PAGETABLE_ORDER;
> -do {
> -mfn = alloc_boot_pages(step, step);
> -} while ( !mfn && (step >>= PAGETABLE_ORDER) );
> -if ( !mfn )
> -panic("Not enough memory for frame table");
> +mfn = alloc_boot_pages(step, step);
>  map_pages_to_xen(s, mfn, step, PAGE_HYPERVISOR);
>  }
>  
> 

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Re: [Xen-devel] [PATCH 03/27] xen/x86: mm: Don't check alloc_boot_pages return

[Jan Beulich]

>>> On 14.08.17 at 16:23,  wrote:
> The only way alloc_boot_pages will return 0 is during the error case.
> Although, Xen will panic in the error path. So the check in the caller
> is pointless.
> 
> Looking at the loop, my understanding is it will try to allocate in
> smaller chunk if a bigger chunk fail. Given that alloc_boot_pages can
> never check, the loop seems unecessary.

Long, long ago alloc_boot_pages() could return 0 without
panic()-ing or BUG()-ing.

> Signed-off-by: Julien Grall 

This as well as the earlier two patches
Reviewed-by: Jan Beulich 

Jan


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[Xen-devel] [PATCH 03/27] xen/x86: mm: Don't check alloc_boot_pages return

[Julien Grall]

The only way alloc_boot_pages will return 0 is during the error case.
Although, Xen will panic in the error path. So the check in the caller
is pointless.

Looking at the loop, my understanding is it will try to allocate in
smaller chunk if a bigger chunk fail. Given that alloc_boot_pages can
never check, the loop seems unecessary.

Signed-off-by: Julien Grall 

---

Cc: Jan Beulich 
Cc: Andrew Cooper 

I haven't tested this code, only build test it. I can't see how
alloc_boot_pages would return 0 other than the error path.
---
 xen/arch/x86/mm.c | 6 +-
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index f53ca43554..66e337109d 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -200,11 +200,7 @@ static void __init init_frametable_chunk(void *start, void 
*end)
  */
 while ( step && s + (step << PAGE_SHIFT) > e + (4 << PAGE_SHIFT) )
 step >>= PAGETABLE_ORDER;
-do {
-mfn = alloc_boot_pages(step, step);
-} while ( !mfn && (step >>= PAGETABLE_ORDER) );
-if ( !mfn )
-panic("Not enough memory for frame table");
+mfn = alloc_boot_pages(step, step);
 map_pages_to_xen(s, mfn, step, PAGE_HYPERVISOR);
 }
 
-- 
2.11.0


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