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

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Date:   Mon, 8 Mar 2021 10:26:25 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Oscar Salvador <osalvador@...e.de>
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 3/8/21 10:20 AM, Oscar Salvador wrote:
> 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?

Yep, makes sense.  If you rev the series, it would be nice to put that
in the changelog.  But, either way, please keep the Ack!