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[2003:cb:c72f:7100:cede:6433:a77b:41e9]) by smtp.gmail.com with ESMTPSA id v4-20020a5d6784000000b0030fbf253c82sm22235978wru.104.2023.06.19.00.41.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 19 Jun 2023 00:41:17 -0700 (PDT) Message-ID: Date: Mon, 19 Jun 2023 09:41:16 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH stable 5.10] mm/memory_hotplug: extend offline_and_remove_memory() to handle more than one memory block Content-Language: en-US To: mawupeng , gregkh@linuxfoundation.org Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, richard.weiyang@linux.alibaba.com, mst@redhat.com, jasowang@redhat.com, pankaj.gupta.linux@gmail.com, mhocko@kernel.org, osalvador@suse.de References: <20230619065121.1720912-1-mawupeng1@huawei.com> <2023061926-monoxide-pastor-fa3b@gregkh> From: David Hildenbrand Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On 19.06.23 09:22, mawupeng wrote: > > > On 2023/6/19 15:16, Greg KH wrote: >> On Mon, Jun 19, 2023 at 02:51:21PM +0800, Wupeng Ma wrote: >>> From: David Hildenbrand >>> >>> commit 8dc4bb58a146655eb057247d7c9d19e73928715b upstream. >>> >>> virtio-mem soon wants to use offline_and_remove_memory() memory that >>> exceeds a single Linux memory block (memory_block_size_bytes()). Let's >>> remove that restriction. >>> >>> Let's remember the old state and try to restore that if anything goes >>> wrong. While re-onlining can, in general, fail, it's highly unlikely to >>> happen (usually only when a notifier fails to allocate memory, and these >>> are rather rare). >>> >>> This will be used by virtio-mem to offline+remove memory ranges that are >>> bigger than a single memory block - for example, with a device block >>> size of 1 GiB (e.g., gigantic pages in the hypervisor) and a Linux memory >>> block size of 128MB. >>> >>> While we could compress the state into 2 bit, using 8 bit is much >>> easier. >>> >>> This handling is similar, but different to acpi_scan_try_to_offline(): >>> >>> a) We don't try to offline twice. I am not sure if this CONFIG_MEMCG >>> optimization is still relevant - it should only apply to ZONE_NORMAL >>> (where we have no guarantees). If relevant, we can always add it. >>> >>> b) acpi_scan_try_to_offline() simply onlines all memory in case >>> something goes wrong. It doesn't restore previous online type. Let's do >>> that, so we won't overwrite what e.g., user space configured. >>> >>> Reviewed-by: Wei Yang >>> Cc: "Michael S. Tsirkin" >>> Cc: Jason Wang >>> Cc: Pankaj Gupta >>> Cc: Michal Hocko >>> Cc: Oscar Salvador >>> Cc: Wei Yang >>> Cc: Andrew Morton >>> Signed-off-by: David Hildenbrand >>> Link: https://lore.kernel.org/r/20201112133815.13332-28-david@redhat.com >>> Signed-off-by: Michael S. Tsirkin >>> Acked-by: Andrew Morton >>> Signed-off-by: Ma Wupeng >>> --- >>> mm/memory_hotplug.c | 105 +++++++++++++++++++++++++++++++++++++------- >>> 1 file changed, 89 insertions(+), 16 deletions(-) >>> >> >> Why is this needed in 5.10.y? Looks like a new feature to me, what >> problem does it solve there? >> >> thanks, >> >> greg k-h > > It do introduce a new feature. But at the same time, it fix a memleak introduced > in Commit 08b3acd7a68f ("mm/memory_hotplug: Introduce offline_and_remove_memory()" > > Our test find a memleak in init_memory_block, it is clear that mem is never > been released due to wrong refcount. Commit 08b3acd7a68f ("mm/memory_hotplug: > Introduce offline_and_remove_memory()") failed to dec refcount after > find_memory_block which fail to dec refcount to zero in remove memory > causing the leak. > > Commit 8dc4bb58a146 ("mm/memory_hotplug: extend offline_and_remove_memory() > to handle more than one memory block") introduce walk_memory_blocks to > replace find_memory_block which dec refcount by calling put_device after > find_memory_block_by_id. In the way, the memleak is fixed. > > Here is the simplified calltrace: > > kmem_cache_alloc_trace+0x664/0xed0 > init_memory_block+0x8c/0x170 > create_memory_block_devices+0xa4/0x150 > add_memory_resource+0x188/0x530 > __add_memory+0x78/0x104 > add_memory+0x6c/0xb0 > Makes sense to me. Of course, we could think about a simplified stable fix that only drops the ref. -- Cheers, David / dhildenb