Re: [PATCH] mem: skip memory locking on failure

[Panu Matilainen <pmatilai@redhat.com>]

On 06/14/2016 05:12 PM, Olivier MATZ wrote:
> Hi Panu,
>
> On 06/14/2016 03:21 PM, Panu Matilainen wrote:
>> On 06/13/2016 01:26 PM, Olivier Matz wrote:
>>> Since recently [1], it is not possible to run the dpdk with user
>>> (non-root) privileges and the --no-huge option. This is because the eal
>>> layer tries to lock the memory. Using locked memory is mandatory for
>>> physical devices because they reference physical addresses.
>>>
>>> But a user may want to start the dpdk without locked memory, because he
>>> does not have the permission to do so, and/or does not have this need.
>>>
>>> Moreover, the option --no-huge is still not functional today since the
>>> physical memory address is not properly filled, so the initial patch is
>>> not really useful.
>>>
>>> This commit fixes this issue by retrying the mmap() wihout the
>>> MAP_LOCKED flag if the first mmap() failed.
>>>
>>> [1] http://www.dpdk.org/ml/archives/dev/2016-May/039404.html
>>>
>>> Fixes: 593a084afc2b ("mem: lock pages when not using hugepages")
>>> Reported-by: Panu Matilainen <pmatilai@redhat.com>
>>> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
>>> ---
>>>  lib/librte_eal/linuxapp/eal/eal_memory.c | 9 +++++++++
>>>  1 file changed, 9 insertions(+)
>>>
>>> diff --git a/lib/librte_eal/linuxapp/eal/eal_memory.c
>>> b/lib/librte_eal/linuxapp/eal/eal_memory.c
>>> index 79d1d2d..08692d1 100644
>>> --- a/lib/librte_eal/linuxapp/eal/eal_memory.c
>>> +++ b/lib/librte_eal/linuxapp/eal/eal_memory.c
>>> @@ -1075,6 +1075,15 @@ rte_eal_hugepage_init(void)
>>>      if (internal_config.no_hugetlbfs) {
>>>          addr = mmap(NULL, internal_config.memory, PROT_READ |
>>> PROT_WRITE,
>>>              MAP_LOCKED | MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
>>> +        /* retry without MAP_LOCKED */
>>> +        if (addr == MAP_FAILED && errno == EAGAIN) {
>>> +            addr = mmap(NULL, internal_config.memory,
>>> +                PROT_READ | PROT_WRITE,
>>> +                MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
>>> +            if (addr != MAP_FAILED)
>>> +                RTE_LOG(NOTICE, EAL,
>>> +                    "Cannot lock memory: don't use physical
>>> devices\n");
>>> +        }
>>>          if (addr == MAP_FAILED) {
>>>              RTE_LOG(ERR, EAL, "%s: mmap() failed: %s\n", __func__,
>>>                      strerror(errno));
>>>
>>
>> I'm not really that familiar with dpdk memory usage, but gut feeling
>> says such a thing needs to be explicit - either you explicitly ask for
>> memory that doesn't need to be locked, or this simply fails with no
>> retries. Or something like that. But "maybe I did, maybe I didn't"
>> doesn't seem like very good API semantics to me :)
>
> Yes, you're right. Anyway as this commit is not useful today,
> it would be better to revert it.

I suppose you mean revert the memlock commit, ie this?

commit 593a084afc2b441895aeca78a2c4465e450d0ef5
Author: Olivier Matz <olivier.matz@6wind.com>
Date:   Wed May 18 13:04:42 2016 +0200

     mem: lock pages when not using hugepages

Reverting that would help in the sense that then we could make the 
test-suite runnable by regular users (I've some patches for this), and 
once that is in place it would sort of force dealing with the issue one 
way or the other in future work in this area :)

>
>> Are there actual plans to make --no-huge work with real devices?
>
> I think this is something that could be part of the memory
> rework referenced by Thomas:
> http://dpdk.org/ml/archives/dev/2016-April/037444.html
>
> I don't know if it's planified yet.
>
>
>> If not then documenting --no-huge to imply unlocked memory is one
>> option I guess.
>
> There is already some words in the known issues:
> http://dpdk.org/doc/guides/rel_notes/known_issues.html?highlight=known%20issues#pmd-does-not-work-with-no-huge-eal-command-line-parameter

Right, so it wouldn't be a regression at least.

	- Panu -

>
> Maybe we could add something somewhere else, but I did not find
> any doc referencing eal options. Only a guide for testpmd here:
> http://dpdk.org/doc/guides/testpmd_app_ug/run_app.html#eal-command-line-options
>
>
> John, maybe you have an idea?
>
> Thanks
> Olivier
>