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Subject: Re: [PATCH v3 3/4] hugetlbfs: remove hugetlb_add_hstate() warning for
 existing hstate
To:     "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
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Cc:     Catalin Marinas <catalin.marinas@arm.com>,
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        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
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        Albert Ou <aou@eecs.berkeley.edu>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        "David S.Miller" <davem@davemloft.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Longpeng <longpeng2@huawei.com>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        Randy Dunlap <rdunlap@infradead.org>,
        Mina Almasry <almasrymina@google.com>,
        Peter Xu <peterx@redhat.com>,
        Nitesh Narayan Lal <nitesh@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>
References: <20200417185049.275845-1-mike.kravetz@oracle.com>
 <20200417185049.275845-4-mike.kravetz@oracle.com>
 <87blnj4x9p.fsf@linux.ibm.com>
From:   Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <d39a33da-6095-c616-6bff-6af8795922d1@oracle.com>
Date:   Wed, 22 Apr 2020 09:56:03 -0700
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On 4/22/20 3:42 AM, Aneesh Kumar K.V wrote:
> Mike Kravetz <mike.kravetz@oracle.com> writes:
> 
>> The routine hugetlb_add_hstate prints a warning if the hstate already
>> exists.  This was originally done as part of kernel command line
>> parsing.  If 'hugepagesz=' was specified more than once, the warning
>> 	pr_warn("hugepagesz= specified twice, ignoring\n");
>> would be printed.
>>
>> Some architectures want to enable all huge page sizes.  They would
>> call hugetlb_add_hstate for all supported sizes.  However, this was
>> done after command line processing and as a result hstates could have
>> already been created for some sizes.  To make sure no warning were
>> printed, there would often be code like:
>> 	if (!size_to_hstate(size)
>> 		hugetlb_add_hstate(ilog2(size) - PAGE_SHIFT)
>>
>> The only time we want to print the warning is as the result of command
>> line processing.
> 
> Does this patch break hugepages=x command line? I haven't tested this
> yet. But one of the details w.r.t. skipping that hugetlb_add_hstate is
> to make sure we can configure the max_huge_pages. 
> 

Are you asking about hugepages=x being the only option on the command line?
If so, then the behavior is not changed.  This will result in x pages of
default huge page size being allocated.  Where default huge page size is of
course architecture dependent.  On an x86 VM,

[    0.040474] Kernel command line: BOOT_IMAGE=/vmlinuz-5.6.0-mm1+ root=/dev/mapper/fedora_new--host-root ro rd.lvm.lv=fedora_new-host/root rd.lvm.lv=fedora_new-host/swap console=tty0 console=ttyS0,115200 audit=0 transparent_hugepage=always hugepages=128
[    0.332618] HugeTLB registered 1.00 GiB page size, pre-allocated 0 pages
[    0.333245] HugeTLB registered 2.00 MiB page size, pre-allocated 128 pages

BTW - Here are the command line options I tested on x86 with this series.

No errors or warnings
---------------------
hugepages=128
hugepagesz=2M hugepages=128
default_hugepagesz=2M hugepages=128
hugepages=128 default_hugepagesz=2M
hugepagesz=1G hugepages=2
hugepages=2 default_hugepagesz=1G
default_hugepagesz=1G hugepages=2
hugepages=128 hugepagesz=1G hugepages=2
hugepagesz=1G hugepages=2 hugepagesz=2M hugepages=128
default_hugepagesz=2M hugepages=128 hugepagesz=1G hugepages=2
hugepages=128 default_hugepagesz=2M hugepagesz=1G hugepages=2
hugepages=2 default_hugepagesz=1G hugepagesz=2M hugepages=128
default_hugepagesz=1G hugepages=2 hugepagesz=2M hugepages=128
default_hugepagesz=2M hugepagesz=2M hugepages=128
default_hugepagesz=2M hugepagesz=1G hugepages=2 hugepagesz=2M hugepages=128

Error or warning
----------------
hugepages=128 hugepagesz=2M hugepages=256
hugepagesz=2M hugepages=128 hugepagesz=2M hugepages=256
default_hugepagesz=2M hugepages=128 hugepagesz=2M hugepages=256
hugepages=128 hugepages=256
hugepagesz=2M hugepages=128 hugepages=2 default_hugepagesz=1G

-- 
Mike Kravetz