Date:   Mon, 10 Jan 2022 00:31:10 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc:     linux-mm@kvack.org, John Hubbard <jhubbard@nvidia.com>,
        Christoph Hellwig <hch@infradead.org>,
        William Kucharski <william.kucharski@oracle.com>,
        linux-kernel@vger.kernel.org, Jason Gunthorpe <jgg@ziepe.ca>
Subject: Re: [PATCH v2 08/28] gup: Handle page split race more efficiently
Message-ID: <YdvuzvdoYz1KzFWo@infradead.org>
References: <20220110042406.499429-1-willy@infradead.org>
 <20220110042406.499429-9-willy@infradead.org>
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On Mon, Jan 10, 2022 at 04:23:46AM +0000, Matthew Wilcox (Oracle) wrote:
> If we hit the page split race, the current code returns NULL which will
> presumably trigger a retry under the mmap_lock.  This isn't necessary;
> we can just retry the compound_head() lookup.  This is a very minor
> optimisation of an unlikely path, but conceptually it matches (eg)
> the page cache RCU-protected lookup.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>