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a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1683925435; bh=nqsLqlAN3czrFKPz/1Q7lmk66avDWHKVM8stcgmsqnY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=dFurDZZ/2x+jDThsWcbS37/WKCuCQ+sxDT+RC8KQoC23sQUhCwQdv2nUcq6VVmy9A efV/5NN1FwC33xgoQvFGoyVgwRAgRnC04ZvhCYqP5H7mgosf8ymMzLSMiUCh48D7Ly qG/7aY6Va0IWB0H/p9UsBjOlca1sq49eWSpIwBE4= Date: Fri, 12 May 2023 14:03:53 -0700 From: Andrew Morton To: Junxiao Chang Cc: kirill.shutemov@linux.intel.com, mhocko@suse.com, jmarchan@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, mike.kravetz@oracle.com, muchun.song@linux.dev Subject: Re: [PATCH] mm: fix hugetlb page unmap count balance issue Message-Id: <20230512140353.8b95e8cb024c8e7a1a3b03c1@linux-foundation.org> In-Reply-To: <20230512072036.1027784-1-junxiao.chang@intel.com> References: <20230512072036.1027784-1-junxiao.chang@intel.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: 9baos93fygbtroi8f7jp9wxnjtpub41i X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A56301C0007 X-HE-Tag: 1683925436-464634 X-HE-Meta: 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 CiSG2IVA t4VDBI2YlU2XebZDv1LczOzvZiUxsdwd9oiGviWWSTix24msHTsAMY7HIyDoqSenLpxNW3EUZHTb6razSuXIp8wVE9CE3VrQECN2y814huO6aCHC7VT97lvI6zeKGhx+kNEslyC3Aw2iXJQ2KEeCu6dymt4qwB+e5F6osxNxuhK6jCGjfS9N93yqJcEMbjyJvo3GFzXDQ61xQZ8mtaFyZiVANEU0kLhEd+usbi1hZoOX7G9yLBgq4MhxFrdwOhaAkiMLtwgpji82aLsy4xfrHI1vAkzYgmmkFV2oEqkNi8HjoUuVaSVZLvpAEf0pTK/ck2DxoRrwH3omnj/xpbq94WWqFSu9B8n8z1RsK X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, 12 May 2023 15:20:36 +0800 Junxiao Chang wrote: > hugetlb page usually is mapped with pmd, but occasionally it might be > mapped with pte. QEMU can use udma-buf to create host dmabufs for guest > framebuffers. When QEMU is launched with parameter "hugetlb=on", > udmabuffer driver maps hugetlb page with pte in page fault handler. Are there any other situations in which a hugetlb page is mapped in this fashion? If not, can QEMU be changed to map with a pmd? So we get one less weird special case in MM.