linux-kernel - Re: [PATCH v3 2/8] mm/mprotect: Remove NUMA_HUGE_PTE

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Message-ID: <054324a3-bc77-426f-a751-06700aad394e@redhat.com>
Date: Tue, 6 Aug 2024 15:02:00 +0200
From: David Hildenbrand <david@...hat.com>
To: Peter Xu <peterx@...hat.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Dave Jiang <dave.jiang@...el.com>, Rik van Riel <riel@...riel.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Michael Ellerman <mpe@...erman.id.au>, linuxppc-dev@...ts.ozlabs.org,
 Matthew Wilcox <willy@...radead.org>,
 Rick P Edgecombe <rick.p.edgecombe@...el.com>,
 Oscar Salvador <osalvador@...e.de>, Mel Gorman
 <mgorman@...hsingularity.net>, Andrew Morton <akpm@...ux-foundation.org>,
 Borislav Petkov <bp@...en8.de>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Huang Ying <ying.huang@...el.com>, "Kirill A . Shutemov"
 <kirill@...temov.name>, "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
 Dan Williams <dan.j.williams@...el.com>, Thomas Gleixner
 <tglx@...utronix.de>, Hugh Dickins <hughd@...gle.com>, x86@...nel.org,
 Nicholas Piggin <npiggin@...il.com>, Vlastimil Babka <vbabka@...e.cz>,
 Ingo Molnar <mingo@...hat.com>, Alex Thorlton <athorlton@....com>
Subject: Re: [PATCH v3 2/8] mm/mprotect: Remove NUMA_HUGE_PTE_UPDATES

> Right.
> 
> I don't have a reason to change numa_pte_updates semantics yet so far, but
> here there's the problem where numa_huge_pte_updates can be ambiguous when
> there is even PUD involved.
> 
> In general, I don't know how I should treat this counter in PUD path even
> if NUMA isn't involved in dax yet; it can be soon involved if we move on
> with using this same path for hugetlb, or when 1G thp can be possible (with
> Yu Zhao's TAO?).

We shouldn't bother about it in the PUD path at all I think. Especially 
as long as NUMA hinting doesn't apply to any of what we would handle on 
the PUD path :)

> 
> One other thing I can do is I drop this patch, ignore NUMA_HUGE_PTE_UPDATES
> in PUD dax processing for now.  It'll work for this series, but it'll still
> be a problem later.  I figured maybe we should simply drop it from now.

It probably shouldn't block your other fixes and we should likely 
discuss that separately.

I agree that we should look into dropping that PMD counter completely.

-- 
Cheers,

David / dhildenb