netdev - Re: [PATCH 0/6 v3] kvmalloc

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Message-ID: <20170130162822.GC4664@dhcp22.suse.cz>
Date:   Mon, 30 Jan 2017 17:28:22 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Daniel Borkmann <daniel@...earbox.net>
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 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.
-- 
Michal Hocko
SUSE Labs