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

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Date:   Sat, 9 Apr 2022 13:43:49 +0200
From:   Thorsten Leemhuis <regressions@...mhuis.info>
To:     Song Liu <song@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, linux-mm@...ck.org
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        kernel-team@...com, akpm@...ux-foundation.org,
        rick.p.edgecombe@...el.com, hch@...radead.org,
        imbrenda@...ux.ibm.com
Subject: Re: [PATCH bpf 0/2] vmalloc: bpf: introduce VM_ALLOW_HUGE_VMAP

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.