linux-kernel - Re: [PATCH 0/6] Boot-time switching between 4- and 5-level paging for 4.15, Part 1

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Date:   Fri, 20 Oct 2017 15:18:07 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Borislav Petkov <bp@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] Boot-time switching between 4- and 5-level paging
 for 4.15, Part 1

On Fri, Oct 20, 2017 at 02:49:13AM -0700, Minchan Kim wrote:
> Hi Ingo,
> 
> On Fri, Oct 20, 2017 at 10:18:53AM +0200, Ingo Molnar wrote:
> > 
> > * Kirill A. Shutemov <kirill@...temov.name> wrote:
> > 
> > > On Tue, Oct 03, 2017 at 11:27:54AM +0300, Kirill A. Shutemov wrote:
> > > > On Fri, Sep 29, 2017 at 05:08:15PM +0300, Kirill A. Shutemov wrote:
> > > > > The first bunch of patches that prepare kernel to boot-time switching
> > > > > between paging modes.
> > > > > 
> > > > > Please review and consider applying.
> > > > 
> > > > Ping?
> > > 
> > > Ingo, is there anything I can do to get review easier for you?
> > 
> > Yeah, what is the conclusion on the sub-discussion of patch #2:
> > 
> >   [PATCH 2/6] mm/zsmalloc: Prepare to variable MAX_PHYSMEM_BITS
> > 
> > ... do we want to skip it entirely and use the other 5 patches?
> 
> Sorry for the too much late reply, Kirill.
> Yes, you can skip it.
> 
> As Nitin said in that patch's thread, zsmalloc has assumed
> PFN_BIT is (BITS_PER_LONG - PAGE_SHIFT) so it already covers
> X86_5LEVEL well, I think.
> 
> In summary, there is no need to change it.
> I hope it helps to merge this patchset series.

Acctually, no, we need something.

The problem is that later in the series[1] we make MAX_PHYSMEM_BITS
dynamic. It's not a simple constant anymore.

But zsmalloc uses it to define _PFN_BIT, which, with few hoops, defines
ZS_SIZE_CLASSES. ZS_SIZE_CLASSES is used to specify size of a field in
'struct zs_pool' and build fails if it's not constant.

My patch addresses this, but there are more than one solution to the
problem.

Which way do you prefer to get it fixed?

[1] https://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git/commit/?h=la57/boot-switching/v8&id=57f669244fab9081a4343b59373ff43170ef328f

-- 
 Kirill A. Shutemov