linux-kernel - Re: [PATCH 0/6 v3] kvmalloc

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Date:   Mon, 30 Jan 2017 17:45:03 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        marcelo.leitner@...il.com
Subject: Re: [PATCH 0/6 v3] kvmalloc

On 01/30/2017 05:28 PM, Michal Hocko wrote:
> On Mon 30-01-17 17:15:08, Daniel Borkmann wrote:
>> On 01/30/2017 08:56 AM, Michal Hocko wrote:
>>> On Fri 27-01-17 21:12:26, Daniel Borkmann wrote:
>>>> On 01/27/2017 11:05 AM, Michal Hocko wrote:
>>>>> On Thu 26-01-17 21:34:04, Daniel Borkmann wrote:
>>> [...]
>>>>>> So to answer your second email with the bpf and netfilter hunks, why
>>>>>> not replacing them with kvmalloc() and __GFP_NORETRY flag and add that
>>>>>> big fat FIXME comment above there, saying explicitly that __GFP_NORETRY
>>>>>> is not harmful though has only /partial/ effect right now and that full
>>>>>> support needs to be implemented in future. That would still be better
>>>>>> that not having it, imo, and the FIXME would make expectations clear
>>>>>> to anyone reading that code.
>>>>>
>>>>> Well, we can do that, I just would like to prevent from this (ab)use
>>>>> if there is no _real_ and _sensible_ usecase for it. Having a real bug
>>>>
>>>> Understandable.
>>>>
>>>>> report or a fallback mechanism you are mentioning above would justify
>>>>> the (ab)use IMHO. But that abuse would be documented properly and have a
>>>>> real reason to exist. That sounds like a better approach to me.
>>>>>
>>>>> But if you absolutely _insist_ I can change that.
>>>>
>>>> Yeah, please do (with a big FIXME comment as mentioned), this originally
>>>> came from a real bug report. Anyway, feel free to add my Acked-by then.
>>>
>>> Thanks! I will repost the whole series today.
>>
>> Looks like I got only Cc'ed on the cover letter of your v3 from today
>> (should have been v4 actually?).
>
> Yes
>
>> Anyway, I looked up the last patch
>> on lkml [1] and it seems you forgot the __GFP_NORETRY we talked about?
>
> I misread your response. I thought you were OK with the FIXME
> explanation.
>
>> At least that was what was discussed above (insisting on __GFP_NORETRY
>> plus FIXME comment) for providing my Acked-by then. Can you still fix
>> that up in a final respin?
>
> I will probably just drop that last patch instead. I am not convinced
> that we should bend the new API over and let people mimic that
> throughout the code. I have just seen too many examples of this pattern
> already.
>
> I would also like to prevent the next rebase, unless there any issues
> with some patches of course.

Ok, I'm fine with that as well.

Thanks,
Daniel