From: Julien Grall <julien@xen.org>
To: Jan Beulich <jbeulich@suse.com>
Cc: Julien Grall <jgrall@amazon.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
George Dunlap <george.dunlap@citrix.com>,
Ian Jackson <iwj@xenproject.org>,
Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
xen-devel@lists.xenproject.org
Subject: Re: [PATCH] xen/page_alloc: Remove dead code in alloc_domheap_pages()
Date: Sun, 25 Apr 2021 14:41:04 +0100 [thread overview]
Message-ID: <6b37dc84-a251-a9d7-071d-65d2afad6361@xen.org> (raw)
In-Reply-To: <6d3593cb-40d4-df17-4070-a6c18ea7d62b@suse.com>
Hi Jan,
On 07/04/2021 10:25, Jan Beulich wrote:
> On 06.04.2021 21:22, Julien Grall wrote:
>> --- a/xen/common/page_alloc.c
>> +++ b/xen/common/page_alloc.c
>> @@ -457,6 +457,12 @@ static long total_avail_pages;
>> static DEFINE_SPINLOCK(heap_lock);
>> static long outstanding_claims; /* total outstanding claims by all domains */
>>
>> +static void __init __maybe_unused build_assertions(void)
>> +{
>> + /* Zone 0 is reserved for Xen, so we at least need two zones to function.*/
>> + BUILD_BUG_ON(NR_ZONES < 2);
>> +}
>
> With a couple of transformations this could also be
>
> BUILD_BUG_ON(PADDR_BITS <= PAGE_SHIFT);
>
> i.e. you're checking that the architecture allows for at least two
> pages to be addressable. Is this really a useful thing to check?
I saw it, but I was concerned that someone may modify the definition of
NR_ZONES without looking at the rest of the code base.
Anyway, I guess that the ASSERT(zone_hi != 0) in the code should be
sufficient to catch such problem. So I will drop it.
>
> Irrespective of the usefulness, if this is to be kept I think the
> function wants to live at the end of the source file, like the
> majority of other files have it (another consistent place could
> be at the top of the file, after all #include-s, as can be found
> in two other cases).
>
>> @@ -2340,8 +2346,9 @@ struct page_info *alloc_domheap_pages(
>>
>> bits = domain_clamp_alloc_bitsize(memflags & MEMF_no_owner ? NULL : d,
>> bits ? : (BITS_PER_LONG+PAGE_SHIFT));
>> - if ( (zone_hi = min_t(unsigned int, bits_to_zone(bits), zone_hi)) == 0 )
>> - return NULL;
>> +
>> + zone_hi = min_t(unsigned int, bits_to_zone(bits), zone_hi);
>> + ASSERT(zone_hi != 0);
>
> With the function above preferably dropped or at least moved,
> Reviewed-by: Jan Beulich <jbeulich@suse.com>
>
> I'd like to point out though that I think this would be a good
> opportunity to eliminate the use of min_t() here, by changing
> bits_to_zone()'s 1 to 1u. But I suppose you again would prefer
> to not make this extra change right here, despite it being
> somewhat related to bits_to_zone() only ever returning positive
> values.
In general, I am in not in favor to modify unrelated to code (e.g.
coding style) or things that deserved a more than a one-line explanation
in the commit message. This is not the case here, so I will respin it
and switch from min_t to min.
Cheers,
--
Julien Grall
prev parent reply other threads:[~2021-04-25 13:41 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-06 19:22 [PATCH] xen/page_alloc: Remove dead code in alloc_domheap_pages() Julien Grall
2021-04-07 9:25 ` Jan Beulich
2021-04-25 13:41 ` Julien Grall [this message]
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