linux-kernel - Re: [PATCH 1/3] hugetlbfs: extend hugetlb_vma

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Date:   Mon, 25 Sep 2023 15:25:01 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     riel@...riel.com
Cc:     linux-kernel@...r.kernel.org, kernel-team@...a.com,
        linux-mm@...ck.org, akpm@...ux-foundation.org,
        muchun.song@...ux.dev, leit@...a.com, willy@...radead.org
Subject: Re: [PATCH 1/3] hugetlbfs: extend hugetlb_vma_lock to private VMAs

On 09/25/23 16:28, riel@...riel.com wrote:
> From: Rik van Riel <riel@...riel.com>
> 
> Extend the locking scheme used to protect shared hugetlb mappings
> from truncate vs page fault races, in order to protect private
> hugetlb mappings (with resv_map) against MADV_DONTNEED.

The only time an anon hugetlb mapping would not have a resv_map would
be in the case where MAP_NORESERVE was specified.  In this case the user
should be prepared for allocation failures.  I am good with this approach
not adding locking for the MAP_NORESERVE case.

> Add a read-write semaphore to the resv_map data structure, and
> use that from the hugetlb_vma_(un)lock_* functions, in preparation
> for closing the race between MADV_DONTNEED and page faults.
> 
> Signed-off-by: Rik van Riel <riel@...riel.com>
> ---
>  include/linux/hugetlb.h |  6 ++++++
>  mm/hugetlb.c            | 41 +++++++++++++++++++++++++++++++++++++----
>  2 files changed, 43 insertions(+), 4 deletions(-)

Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>

-- 
Mike Kravetz