linux-kernel - Re: [PATCH v4 1/3] x86/vmemmap: Drop handling of 4K unaligned vmemmap range

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Message-ID: <20210308182031.GA25767@linux>
Date:   Mon, 8 Mar 2021 19:20:40 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/3] x86/vmemmap: Drop handling of 4K unaligned
 vmemmap range

On Thu, Mar 04, 2021 at 07:50:10AM -0800, Dave Hansen wrote:
> On 3/1/21 12:32 AM, Oscar Salvador wrote:
> > remove_pte_table() is prepared to handle the case where either the
> > start or the end of the range is not PAGE aligned.
> > This cannot actually happen:
> > 
> > __populate_section_memmap enforces the range to be PMD aligned,
> > so as long as the size of the struct page remains multiple of 8,
> > the vmemmap range will be aligned to PAGE_SIZE.
> > 
> > Drop the dead code and place a VM_BUG_ON in vmemmap_{populate,free}
> > to catch nasty cases.
> 
> I was wondering why the VM_BUG_ON()s went in vmemmap_free() instead of
> closer to the code that you modified in remove_pte_table().  I assume
> this was because vmemmap_free() is the only (indirect) caller of
> remove_pte_table().

Yes, that was pretty much the reason.
It seemed reasonable to me to fence it off at the "gate", and not further
deep.

Does it make sense to you? May I keep your Ack?

Thanks Dave!

> 
> Otherwise, this looks fine to me:
> 
> Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
> 

-- 
Oscar Salvador
SUSE L3