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[73.69.118.222]) by smtp.gmail.com with ESMTPSA id a9sm391871qkk.39.2021.01.19.17.43.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Jan 2021 17:43:48 -0800 (PST) From: Pavel Tatashin To: pasha.tatashin@soleen.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, vbabka@suse.cz, mhocko@suse.com, david@redhat.com, osalvador@suse.de, dan.j.williams@intel.com, sashal@kernel.org, tyhicks@linux.microsoft.com, iamjoonsoo.kim@lge.com, mike.kravetz@oracle.com, rostedt@goodmis.org, mingo@redhat.com, jgg@ziepe.ca, peterz@infradead.org, mgorman@suse.de, willy@infradead.org, rientjes@google.com, jhubbard@nvidia.com, linux-doc@vger.kernel.org, ira.weiny@intel.com, linux-kselftest@vger.kernel.org Subject: [PATCH v6 08/14] mm/gup: do not migrate zero page Date: Tue, 19 Jan 2021 20:43:27 -0500 Message-Id: <20210120014333.222547-9-pasha.tatashin@soleen.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210120014333.222547-1-pasha.tatashin@soleen.com> References: <20210120014333.222547-1-pasha.tatashin@soleen.com> MIME-Version: 1.0 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: On some platforms ZERO_PAGE(0) might end-up in a movable zone. Do not migrate zero page in gup during longterm pinning as migration of zero pag= e is not allowed. For example, in x86 QEMU with 16G of memory and kernelcore=3D5G parameter= , I see the following: Boot#1: zero_pfn 0x48a8d zero_pfn zone: ZONE_DMA32 Boot#2: zero_pfn 0x20168d zero_pfn zone: ZONE_MOVABLE On x86, empty_zero_page is declared in .bss and depending on the loader may end up in different physical locations during boots. Signed-off-by: Pavel Tatashin --- include/linux/mmzone.h | 4 ++++ mm/gup.c | 2 ++ 2 files changed, 6 insertions(+) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index fc99e9241846..f67427a8f22b 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -427,6 +427,10 @@ enum zone_type { * techniques might use alloc_contig_range() to hide previously * exposed pages from the buddy again (e.g., to implement some sort * of memory unplug in virtio-mem). + * 6. ZERO_PAGE(0), kernelcore/movablecore setups might create + * situations where ZERO_PAGE(0) which is allocated differently + * on different platforms may end up in a movable zone. ZERO_PAGE(0) + * cannot be migrated. * * In general, no unmovable allocations that degrade memory offlining * should end up in ZONE_MOVABLE. Allocators (like alloc_contig_range()= ) diff --git a/mm/gup.c b/mm/gup.c index 857b273e32ac..fdd5cda30a07 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1580,6 +1580,8 @@ static long check_and_migrate_cma_pages(struct mm_s= truct *mm, * of the CMA zone if possible. */ if (is_migrate_cma_page(head)) { + if (is_zero_pfn(page_to_pfn(head))) + continue; if (PageHuge(head)) { if (!isolate_huge_page(head, &cma_page_list)) isolation_error_count++; --=20 2.25.1