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Date:   Mon, 20 Apr 2020 12:33:10 -0700
From:   Matthew Wilcox <willy@infradead.org>
To:     Michel Lespinasse <walken@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        linux-mm <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
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        Vlastimil Babka <vbabka@suse.cz>,
        Liam Howlett <Liam.Howlett@oracle.com>,
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        Hugh Dickins <hughd@google.com>, Ying Han <yinghan@google.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Daniel Jordan <daniel.m.jordan@oracle.com>
Subject: Re: [PATCH v4 06/10] mmap locking API: convert nested write lock
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Message-ID: <20200420193310.GF5820@bombadil.infradead.org>
References: <20200415004353.130248-1-walken@google.com>
 <20200415004353.130248-7-walken@google.com>
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On Tue, Apr 14, 2020 at 05:43:49PM -0700, Michel Lespinasse wrote:
> @@ -47,7 +48,7 @@ static inline void activate_mm(struct mm_struct *old, struct mm_struct *new)
>  	 * when the new ->mm is used for the first time.
>  	 */
>  	__switch_mm(&new->context.id);
> -	down_write_nested(&new->mmap_sem, 1);
> +	mmap_write_lock_nested(new, 1);

This should have already been using SINGLE_DEPTH_NESTING.  1 is
uninformative.