linux-kernel - Re: [PATCH 1/5] mm,hugetlb: Change mechanism to detect a COW on private mapping

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Message-ID: <51756190-f379-4faa-a4b1-56fd88d776e1@redhat.com>
Date: Fri, 13 Jun 2025 15:52:09 +0200
From: David Hildenbrand <david@...hat.com>
To: Oscar Salvador <osalvador@...e.de>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Muchun Song <muchun.song@...ux.dev>,
 James Houghton <jthoughton@...gle.com>, Peter Xu <peterx@...hat.com>,
 Gavin Guo <gavinguo@...lia.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] mm,hugetlb: Change mechanism to detect a COW on
 private mapping

On 12.06.25 15:46, Oscar Salvador wrote:
> hugetlb_wp() checks whether the process is trying to COW on a private mapping
> in order to know whether the reservation for that address was already consumed
> or not.
> If it was consumed and we are the ownner of the mapping, the folio will have to
> be unmapped from the other processes.
> 
> Currently, that check is done by looking up the folio in the pagecache and
> compare it to the folio which is mapped in our pagetables.
> If it differs, it means we already mapped it privately before, consuming a
> reservation on the way.
> All we are interested in is whether the mapped folio is anonymous, so we can
> simplify and check for that instead.
> 
> Also, we transition from a trylock to a folio_lock, since the former was only
> needed when hugetlb_fault() had to lock both folios, in order to avoid deadlock.
> 
> Closes: https://lore.kernel.org/lkml/20250513093448.592150-1-gavinguo@igalia.com/

If there is a Closes: there should probably be a Fixes: and a Reported-by:

> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> Suggested-by: Peter Xu <peterx@...hat.com>
> ---

Nothing jumped at me, we'll learn if we missed anything soon I guess :)

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb