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Wed, 22 Jun 2022 23:59:27 -0700 (PDT) Date: Thu, 23 Jun 2022 14:59:23 +0800 From: Muchun Song To: Miaohe Lin Cc: akpm@linux-foundation.org, shy828301@gmail.com, willy@infradead.org, zokeefe@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 10/16] mm/huge_memory: check pmd_present first in is_huge_zero_pmd Message-ID: References: <20220622170627.19786-1-linmiaohe@huawei.com> <20220622170627.19786-11-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220622170627.19786-11-linmiaohe@huawei.com> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655967569; a=rsa-sha256; cv=none; b=nLRyfH9JYl8YN9ZPfKT1I3PNmSlBf7l2cMT44gYIvLynH/96aHArhTAbQGN0DtJzfaQXsJ EtD7aAAVVPUpTgH+oNf/4CxBtNf/iqe69hDhTXJihXVMkq6fsGdhpBx3iFDEMs3/dq2iKN VU8neaETSZJkEfPiTq+TnndZHlE2PQA= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655967569; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=eWXRy4yaBbGLOb3VHZrtrJxxwapjIbRhxQbw7lQ4SBk=; b=mkzmBVMAHWrs+DyQUmrmS823dRHUChOmdHZlXki2ZelT/oGNap4M4sYzXYfHmcCO3mpRhf sfQxdpBfrHlY4SQgty7Lcan4TuKoNDvIOK2Ng78zlKxkB0oPk9yeOMbYTin/L/kMoPYoYQ wKpwQJVX7IEII5EIMfTmkk7W2QHoDJI= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=1r5lHudG; dmarc=pass (policy=none) header.from=bytedance.com; spf=pass (imf02.hostedemail.com: domain of songmuchun@bytedance.com designates 209.85.216.42 as permitted sender) smtp.mailfrom=songmuchun@bytedance.com X-Rspam-User: X-Rspamd-Queue-Id: EE26D80002 Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=1r5lHudG; dmarc=pass (policy=none) header.from=bytedance.com; spf=pass (imf02.hostedemail.com: domain of songmuchun@bytedance.com designates 209.85.216.42 as permitted sender) smtp.mailfrom=songmuchun@bytedance.com X-Stat-Signature: hre5r63j7qo46qhi4uqhdndkihgga35i X-Rspamd-Server: rspam09 X-HE-Tag: 1655967568-486659 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 Thu, Jun 23, 2022 at 01:06:21AM +0800, Miaohe Lin wrote: > When pmd is non-present, pmd_pfn returns an insane value. So we should Although it does not cause any problems, it is better to check pmd_present() in advance. The change looks good to me. So > check pmd_present first to avoid acquiring such insane value and also > avoid touching possible cold huge_zero_pfn cache line when pmd isn't > present. > > Signed-off-by: Miaohe Lin Reviewed-by: Muchun Song