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Peter Anvin" , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20210202112450.11932-1-osalvador@suse.de> <20210202112450.11932-2-osalvador@suse.de> From: David Hildenbrand Organization: Red Hat GmbH Subject: Re: [PATCH 1/2] x86/vmemmap: Remove !PAGE_ALIGNED case in remove_pte_table Message-ID: <1d8ca669-6c92-4692-b2c7-1bfaa6f9707e@redhat.com> Date: Tue, 2 Feb 2021 14:20:36 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20210202112450.11932-2-osalvador@suse.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 66004336B615 X-Stat-Signature: i9ajypcjem4ik7adcnmmktez95igmske Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf01; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=63.128.21.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1612272046-87366 Content-Transfer-Encoding: quoted-printable 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: > @@ -962,7 +962,6 @@ remove_pte_table(pte_t *pte_start, unsigned long ad= dr, unsigned long end, > { > unsigned long next, pages =3D 0; > pte_t *pte; > - void *page_addr; > phys_addr_t phys_addr; > =20 > pte =3D pte_start + pte_index(addr); > @@ -983,42 +982,19 @@ remove_pte_table(pte_t *pte_start, unsigned long = addr, unsigned long end, > if (phys_addr < (phys_addr_t)0x40000000) > return; > =20 > - if (PAGE_ALIGNED(addr) && PAGE_ALIGNED(next)) { > - /* > - * Do not free direct mapping pages since they were > - * freed when offlining, or simplely not in use. > - */ > - if (!direct) > - free_pagetable(pte_page(*pte), 0); > - > - spin_lock(&init_mm.page_table_lock); > - pte_clear(&init_mm, addr, pte); > - spin_unlock(&init_mm.page_table_lock); > - > - /* For non-direct mapping, pages means nothing. */ > - pages++; > - } else { > - /* > - * If we are here, we are freeing vmemmap pages since > - * direct mapped memory ranges to be freed are aligned. > - * > - * If we are not removing the whole page, it means > - * other page structs in this page are being used and > - * we canot remove them. So fill the unused page_structs > - * with 0xFD, and remove the page when it is wholly > - * filled with 0xFD. > - */ > - memset((void *)addr, PAGE_INUSE, next - addr); > + /* > + * Do not free direct mapping pages since they were > + * freed when offlining, or simplely not in use. > + */ s/simplely/simply/ (I know, not your fault :) ) However, that comment is highly confusing. There is nothing to free in=20 case of the a direct mapping; we never allocated anything. That's how a=20 direct map works. I'd just get rid of the comment completely - we also don't have one at=20 the other "if (!direct)" places. (side note: all this freeing before unmapping looks very weird, but at=20 least we should have valid accesses anymore) > + if (!direct) > + free_pagetable(pte_page(*pte), 0); [...] > { > + /* > + * See comment in vmemmap_populate(). > + */ I'd drop this comment ... > + VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE)); > + VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE)); > + > remove_pagetable(start, end, false, altmap); > } > =20 > @@ -1556,6 +1538,15 @@ int __meminit vmemmap_populate(unsigned long sta= rt, unsigned long end, int node, > { > int err; > =20 > + /* > + * __populate_section_memmap enforces the range to be added to be > + * PMD aligned. Therefore we can be sure that, as long as the > + * struct page size is multiple of 8, the vmemmap range will be > + * PAGE aligned. > + */ ... and this comment, moving the details into the patch description. The commit should be easy to detect using git blame in case anybody=20 wonders why. > + VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE)); > + VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE)); > + > if (end - start < PAGES_PER_SECTION * sizeof(struct page)) > err =3D vmemmap_populate_basepages(start, end, node, NULL); > else if (boot_cpu_has(X86_FEATURE_PSE)) >=20 Apart from that looks good, thanks! --=20 Thanks, David / dhildenb