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Date:   Mon, 30 Aug 2021 15:24:14 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Miaohe Lin <linmiaohe@huawei.com>
Cc:     akpm@linux-foundation.org, vbabka@suse.cz, sfr@canb.auug.org.au,
        peterz@infradead.org, mgorman@techsingularity.net,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 6/6] mm/page_alloc.c: avoid allocating highmem pages via
 alloc_pages_exact_nid()
Message-ID: <YSzqDt/13YbOAyo4@casper.infradead.org>
References: <20210830141051.64090-1-linmiaohe@huawei.com>
 <20210830141051.64090-7-linmiaohe@huawei.com>
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On Mon, Aug 30, 2021 at 10:10:51PM +0800, Miaohe Lin wrote:
> Don't use with __GFP_HIGHMEM because page_address() cannot represent
> highmem pages without kmap(). Newly allocated pages would leak as
> page_address() will return NULL for highmem pages here. But It works
> now because the only caller does not specify __GFP_HIGHMEM now.

This is a misunderstanding of how alloc_pages_exact() /
alloc_pages_exact_nid() work.  You simply can't call them with
GFP_HIGHMEM.

If you really must change anything here,
s/__GFP_COMP/(__GFP_COMP|__GFP_HIGHMEM)/g throughout both
alloc_pages_exact() and alloc_pages_exact_nid().