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Re: [PATCH v4 1/6] xen: do not free reserved memory into heap
- To: Julien Grall <julien@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 17 May 2022 18:07:38 +0200
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- Cc: Wei Chen <Wei.Chen@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Penny Zheng <Penny.Zheng@xxxxxxx>
- Delivery-date: Tue, 17 May 2022 16:07:42 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17.05.2022 11:28, Julien Grall wrote:
> On 17/05/2022 09:21, Penny Zheng wrote:
>>>> @@ -2653,7 +2657,8 @@ void __init free_staticmem_pages(struct page_info
>>> *pg, unsigned long nr_mfns,
>>>> }
>>>>
>>>> /* In case initializing page of static memory, mark it
>>>> PGC_reserved. */
>>>> - pg[i].count_info |= PGC_reserved;
>>>> + if ( !(pg[i].count_info & PGC_reserved) )
>>>
>>> NIT: I understand the flag may have already been set, but I am not
>>> convinced if
>>> it is worth checking it and then set.
>>>
>>
>> Jan suggested that since we remove the __init from free_staticmem_pages,
>> it's now in preemptable
>> state at runtime, so better be adding this check here.
>
> Well, count_info is already modified within that loop (see
> mark_page_free()). So I think the impact of setting PGC_reserved is
> going to be meaningless.
>
> However... mark_page_free() is going to set count_info to PGC_state_free
> and by consequence clear PGC_reserved. Theferore, in the current
> implementation we always need to re-set PGC_reserved.
Oh, indeed - I didn't pay attention to that aspect. Which then, however,
means that the comment also wants adjusting.
Jan
> So effectively, the "if" is pointless here.
>
> Cheers,
>
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