linux-kernel - Re: [PATCH v1 05/11] mm: convert VM_PFNMAP tracking to pfnmap_track() + pfnmap

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Message-ID: <ec14d3ec-5ec6-46df-a83c-aaf2cb5c255f@redhat.com>
Date: Mon, 28 Apr 2025 22:19:55 +0200
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, x86@...nel.org, intel-gfx@...ts.freedesktop.org,
 dri-devel@...ts.freedesktop.org, linux-trace-kernel@...r.kernel.org,
 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>, "H. Peter Anvin" <hpa@...or.com>,
 Jani Nikula <jani.nikula@...ux.intel.com>,
 Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, Tvrtko Ursulin
 <tursulin@...ulin.net>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Andrew Morton <akpm@...ux-foundation.org>,
 Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
 Pedro Falcato <pfalcato@...e.de>
Subject: Re: [PATCH v1 05/11] mm: convert VM_PFNMAP tracking to pfnmap_track()
 + pfnmap_untrack()

On 28.04.25 21:37, Lorenzo Stoakes wrote:
> On Mon, Apr 28, 2025 at 07:23:18PM +0200, David Hildenbrand wrote:
>> On 28.04.25 18:24, Peter Xu wrote:
>>> On Mon, Apr 28, 2025 at 06:16:21PM +0200, David Hildenbrand wrote:
>>>>> Probably due to what config you have.  E.g., when I'm looking mine it's
>>>>> much bigger and already consuming 256B, but it's because I enabled more
>>>>> things (userfaultfd, lockdep, etc.).
>>>>
>>>> Note that I enabled everything that you would expect on a production system
>>>> (incld. userfaultfd, mempolicy, per-vma locks), so I didn't enable lockep.
>>>
>>> I still doubt whether you at least enabled userfaultfd, e.g., your previous
>>> paste has:
>>>
>>>     struct vm_userfaultfd_ctx  vm_userfaultfd_ctx;   /*   176     0 */
>>>
>>> Not something that matters.. but just in case you didn't use the expected
>>> config file you wanted to use..
>>
>> You're absolutely right. I only briefly rechecked for this purpose here on
>> my notebook, and only looked for the existence of members, not expecting
>> that we have confusing stuff like vm_userfaultfd_ctx.
>>
>> I checked again and the size stays at 192 with allyesconfig and then
>> disabling debug options.
> 
> I think a reasonable case is everything on, except CONFIG_DEBUG_LOCK_ALLOC and I
> don't care about nommu.
> 
> So:
> 
> CONFIG_PER_VMA_LOCK
> CONFIG_SWAP
> CONFIG_MMU (exclude the nommu vm_region field)
> CONFIG_NUMA
> CONFIG_NUMA_BALANCING
> CONFIG_PER_VMA_LOCK
> CONFIG_ANON_VMA_NAME
> __HAVE_PFNMAP_TRACKING

Yes.

And our ugly friend CONFIG_USERFAULTFD

that is

struct vm_userfaultfd_ctx {
	struct userfaultfd_ctx *ctx;
};
#else /* CONFIG_USERFAULTFD */
#define NULL_VM_UFFD_CTX ((struct vm_userfaultfd_ctx) {})
struct vm_userfaultfd_ctx {};
#endif /* CONFIG_USERFAULTFD */

(yes, you made the same mistake as I made when skimming if everything 
relevant was enabled)

> 
> So to be clear - allyesconfig w/o debug gives us this yes? And we don't add a
> cache line? In which case all good :)

Looks like it!

-- 
Cheers,

David / dhildenb