netdev - Re: [PATCH bpf 0/2] vmalloc: bpf: introduce VM_ALLOW_HUGE

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Date:   Sun, 10 Apr 2022 01:36:09 +0000
From:   Song Liu <songliubraving@...com>
To:     Thorsten Leemhuis <regressions@...mhuis.info>
CC:     Song Liu <song@...nel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "andrii@...nel.org" <andrii@...nel.org>,
        Kernel Team <Kernel-team@...com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "rick.p.edgecombe@...el.com" <rick.p.edgecombe@...el.com>,
        "hch@...radead.org" <hch@...radead.org>,
        "imbrenda@...ux.ibm.com" <imbrenda@...ux.ibm.com>
Subject: Re: [PATCH bpf 0/2] vmalloc: bpf: introduce VM_ALLOW_HUGE_VMAP



> On Apr 9, 2022, at 4:43 AM, Thorsten Leemhuis <regressions@...mhuis.info> wrote:
> 
> Hi, this is your Linux kernel regression tracker.
> 
> On 09.04.22 00:34, Song Liu wrote:
>> Enabling HAVE_ARCH_HUGE_VMALLOC on x86_64 and use it for bpf_prog_pack has
>> caused some issues [1], as many users of vmalloc are not yet ready to
>> handle huge pages. To enable a more smooth transition to use huge page
>> backed vmalloc memory, this set replaces VM_NO_HUGE_VMAP flag with an new
>> opt-in flag, VM_ALLOW_HUGE_VMAP. More discussions about this topic can be
>> found at [2].
>> 
>> Patch 1 removes VM_NO_HUGE_VMAP and adds VM_ALLOW_HUGE_VMAP.
>> Patch 2 uses VM_ALLOW_HUGE_VMAP in bpf_prog_pack.
>> 
>> [1] https://lore.kernel.org/lkml/20220204185742.271030-1-song@kernel.org/
>> [2] https://lore.kernel.org/linux-mm/20220330225642.1163897-1-song@kernel.org/
> 
> These patches apparently fix a regression (one that's mentioned in your
> [2]) that I tracked. Hence in the next iteration of your patches could
> you please instead add a 'Link:' tag pointing to the report for anyone
> wanting to look into the backstory in the future, as explained in
> 'Documentation/process/submitting-patches.rst' and
> 'Documentation/process/5.Posting.rst'? E.g. like this:
> 
> "Link:
> https://lore.kernel.org/netdev/14444103-d51b-0fb3-ee63-c3f182f0b546@molgen.mpg.de/"
> 
> Not totally sure, but I guess it needs a Fixes tag as well specifying
> the change that cause this regression (that's "fac54e2bfb5b"). The
> documents mentioned above explain this, too. A "Reported-by" might be
> appropriate as well.
> 
> In anyone wonders why I care: there are internal and publicly used tools
> and scripts out there that reply on proper "Link" tags. I don't known
> how many, but there is at least one public tool I'm running that cares:
> regzbot, my regression tracking bot, which I use to track Linux kernel
> regressions and generate the regression reports sent to Linus. Proper
> "Link:" tags allow the bot to automatically connect regression reports
> with fixes being posted or applied to resolve the particular regression
> -- which makes regression tracking a whole lot easier and feasible for
> the Linux kernel. That's why it's a great help for me if people set
> proper "Link" tags.
> 
> While at it, let me tell regzbot about this thread:
> #regzbot ^backmonitor:
> https://lore.kernel.org/netdev/14444103-d51b-0fb3-ee63-c3f182f0b546@molgen.mpg.de/
> 
> Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
> 
> P.S.: As the Linux kernel's regression tracker I'm getting a lot of
> reports on my table. I can only look briefly into most of them and lack
> knowledge about most of the areas they concern. I thus unfortunately
> will sometimes get things wrong or miss something important. I hope
> that's not the case here; if you think it is, don't hesitate to tell me
> in a public reply, it's in everyone's interest to set the public record
> straight.

Thanks for the reminder. I will add the Fixes tag, and try to work with 
regzbot. 

Song