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Re: [PATCH v3 1/6] xen: do not free reserved memory into heap
- To: Penny Zheng <Penny.Zheng@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 5 May 2022 09:42:20 +0200
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- Cc: Wei Chen <Wei.Chen@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 05 May 2022 07:42:30 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 05.05.2022 07:12, Penny Zheng wrote:
> Hi jan
>
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@xxxxxxxx>
>> Sent: Wednesday, May 4, 2022 9:27 PM
>> To: Penny Zheng <Penny.Zheng@xxxxxxx>
>> Cc: Wei Chen <Wei.Chen@xxxxxxx>; Andrew Cooper
>> <andrew.cooper3@xxxxxxxxxx>; George Dunlap <george.dunlap@xxxxxxxxxx>;
>> Julien Grall <julien@xxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>;
>> Wei
>> Liu <wl@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
>> Subject: Re: [PATCH v3 1/6] xen: do not free reserved memory into heap
>>
>> On 28.04.2022 05:01, Penny Zheng wrote:
>>> --- a/xen/common/page_alloc.c
>>> +++ b/xen/common/page_alloc.c
>>> @@ -1443,6 +1443,10 @@ static void free_heap_pages(
>>>
>>> ASSERT(order <= MAX_ORDER);
>>>
>>> + if ( pg->count_info & PGC_reserved )
>>> + /* Reserved page shall not go back to the heap. */
>>> + return free_staticmem_pages(pg, 1UL << order, need_scrub);
>>
>> With PGC_reserved being zero, the compiler should CSE this call. Hence ...
>>
>
> I assume that you suggest that we remove the stub function and just let
> free_staticmem_pages not guarded by CONFIG_STATIC_MEMORY any more?
No, I' not suggesting to remove the existing guard. I'm only suggesting
to avoid introducing a stub when that's not really needed.
> Hmmmm, on x86, PGC_reserved will be zero as not defined, and CSE will leave
> no caller here. but on arm, CSE could not guard this?
Why would that be? When !CONFIG_STATIC_MEMORY, I'd expect PGC_reserved
to be zero on Arm as well.
Jan
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