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

From: Dave Hansen <dave.hansen@intel.com>
To: Oscar Salvador <osalvador@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	David Hildenbrand <david@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
	Michal Hocko <mhocko@kernel.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 1/3] x86/vmemmap: Drop handling of 4K unaligned vmemmap range
Date: Mon, 8 Mar 2021 10:26:25 -0800	[thread overview]
Message-ID: <e35672ed-3445-2abe-4bed-b339e909f370@intel.com> (raw)
In-Reply-To: <20210308182031.GA25767@linux>

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!