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[99.241.198.116]) by smtp.gmail.com with ESMTPSA id h22-20020a02c736000000b0033792143bf5sm649986jao.67.2022.06.17.07.15.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Jun 2022 07:15:36 -0700 (PDT) Date: Fri, 17 Jun 2022 10:15:34 -0400 From: Peter Xu To: Mike Kravetz Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-ia64@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Muchun Song , Baolin Wang , Michal Hocko , Naoya Horiguchi , James Houghton , Mina Almasry , "Aneesh Kumar K . V" , Anshuman Khandual , Paul Walmsley , Christian Borntraeger , catalin.marinas@arm.com, will@kernel.org, Andrew Morton Subject: Re: [PATCH 1/4] hugetlb: skip to end of PT page mapping when pte not present Message-ID: References: <20220616210518.125287-1-mike.kravetz@oracle.com> <20220616210518.125287-2-mike.kravetz@oracle.com> MIME-Version: 1.0 In-Reply-To: <20220616210518.125287-2-mike.kravetz@oracle.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655475340; a=rsa-sha256; cv=none; b=IXmg7drZNw0UP4JfC1yDM8oj26zK8Eso8tB6yW10UQboUtyA2Ua/yszBtWd9IDJoAvN/6/ 3PGvovPc3YEHAHrFlieTO8+E8IgHrMzOdjKjXhglDgr5uYJ51D42sVlwegkCWCIkrHuVyx 61aQoBh061vccFn7Q1maY0BMm36gp6k= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=exSbu3g2; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf21.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=peterx@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655475340; 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=45WsYeBZBgVP+tO+Yp5wRnejBKTYaIp3okpekaDuC30=; b=28KAbrYQwEpUq1zr/nPXZeETKakkS+cYR4hKsaAuFk4PZSJMXPfPH6nDAT/S8+N78kD/Jo Gcb0k6pYAdkeRgmb/Yu/at0tbYgxJCilUqatyA6910NjXoHdGZ6gUBfklQUv24Rp5OVnFa wLBjWtPSZsZRUIebgIcvNudfzElc4uA= Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=exSbu3g2; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf21.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=peterx@redhat.com X-Rspam-User: X-Stat-Signature: grxh158akr3ffdrpejsymoeza1no1m97 X-Rspamd-Queue-Id: 8C34D1C00B2 X-Rspamd-Server: rspam08 X-HE-Tag: 1655475340-311493 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: Hi, Mike, On Thu, Jun 16, 2022 at 02:05:15PM -0700, Mike Kravetz wrote: > @@ -6877,6 +6896,39 @@ pte_t *huge_pte_offset(struct mm_struct *mm, > return (pte_t *)pmd; > } > > +/* > + * Return a mask that can be used to update an address to the last huge > + * page in a page table page mapping size. Used to skip non-present > + * page table entries when linearly scanning address ranges. Architectures > + * with unique huge page to page table relationships can define their own > + * version of this routine. > + */ > +unsigned long hugetlb_mask_last_page(struct hstate *h) > +{ > + unsigned long hp_size = huge_page_size(h); > + > + switch (hp_size) { > + case P4D_SIZE: > + return PGDIR_SIZE - P4D_SIZE; > + case PUD_SIZE: > + return P4D_SIZE - PUD_SIZE; > + case PMD_SIZE: > + return PUD_SIZE - PMD_SIZE; > + default: Should we add a WARN_ON_ONCE() if it should never trigger? > + break; /* Should never happen */ > + } > + > + return ~(0UL); > +} > + > +#else > + > +/* See description above. Architectures can provide their own version. */ > +__weak unsigned long hugetlb_mask_last_page(struct hstate *h) > +{ > + return ~(0UL); I'm wondering whether it's better to return 0 rather than ~0 by default. Could an arch with !CONFIG_ARCH_WANT_GENERAL_HUGETLB wrongly skip some valid address ranges with ~0, or perhaps I misread? Thanks, -- Peter Xu