linux-kernel - Re: [PATCH v2 1/1] mm: Always release pages to the buddy allocator in memblock_free

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Date:   Fri, 6 Jan 2023 04:12:49 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Aaron Thompson <dev@...ont.org>
Cc:     Mike Rapoport <rppt@...nel.org>, linux-mm@...ck.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andy@...radead.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Darren Hart <dvhart@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Marco Elver <elver@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        kasan-dev@...glegroups.com, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH v2 1/1] mm: Always release pages to the buddy allocator
 in memblock_free_late().


* Aaron Thompson <dev@...ont.org> wrote:

> 
> On 2023-01-05 02:48, Ingo Molnar wrote:
> > * Aaron Thompson <dev@...ont.org> wrote:
> > 
> > > For example, on an Amazon EC2 t3.micro VM (1 GB) booting via EFI:
> > > 
> > > v6.2-rc2:
> > >   # grep -E 'Node|spanned|present|managed' /proc/zoneinfo
> > >   Node 0, zone      DMA
> > >           spanned  4095
> > >           present  3999
> > >           managed  3840
> > >   Node 0, zone    DMA32
> > >           spanned  246652
> > >           present  245868
> > >           managed  178867
> > > 
> > > v6.2-rc2 + patch:
> > >   # grep -E 'Node|spanned|present|managed' /proc/zoneinfo
> > >   Node 0, zone      DMA
> > >           spanned  4095
> > >           present  3999
> > >           managed  3840
> > >   Node 0, zone    DMA32
> > >           spanned  246652
> > >           present  245868
> > >           managed  222816   # +43,949 pages
> > 
> > [ Note the annotation I added to the output - might be useful in the
> > changelog too. ]
> > 
> > So this patch adds around +17% of RAM to this 1 GB virtual system? That
> > looks rather significant ...
> > 
> > Thanks,
> > 
> > 	Ingo
> 
> It is significant, but I wouldn't describe it as being added. I would say
> that the system is currently losing 17% of RAM due to a bug, and this patch
> fixes that bug.

To the end-user gaining +17% [or +3%] extra usable RAM compared to what 
they had before is what matters, and it's a big deal. :-)

Thanks,

	Ingo