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[95.203.13.87]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-53e1b5a4725sm53493e87.162.2024.12.03.05.51.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Dec 2024 05:51:49 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 3 Dec 2024 14:51:47 +0100 To: Kefeng Wang Cc: Uladzislau Rezki , zuoze , Matthew Wilcox , gustavoars@kernel.org, akpm@linux-foundation.org, linux-hardening@vger.kernel.org, linux-mm@kvack.org, keescook@chromium.org Subject: Re: [PATCH -next] mm: usercopy: add a debugfs interface to bypass the vmalloc check. Message-ID: References: <20241203023159.219355-1-zuoze1@huawei.com> <57f9eca2-effc-3a9f-932b-fd37ae6d0f87@huawei.com> <92768fc4-4fe0-f74a-d61c-dde0eb64e2c0@huawei.com> <76995749-1c2e-4f78-9aac-a4bff4b8097f@huawei.com> Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <76995749-1c2e-4f78-9aac-a4bff4b8097f@huawei.com> On Tue, Dec 03, 2024 at 09:45:09PM +0800, Kefeng Wang wrote: > > > On 2024/12/3 21:39, Uladzislau Rezki wrote: > > On Tue, Dec 03, 2024 at 09:30:09PM +0800, Kefeng Wang wrote: > > > > > > > > > On 2024/12/3 21:10, zuoze wrote: > > > > > > > > > > > > 在 2024/12/3 20:39, Uladzislau Rezki 写道: > > > > > On Tue, Dec 03, 2024 at 07:23:44PM +0800, zuoze wrote: > > > > > > We have implemented host-guest communication based on the TUN device > > > > > > using XSK[1]. The hardware is a Kunpeng 920 machine (ARM architecture), > > > > > > and the operating system is based on the 6.6 LTS version with kernel > > > > > > version 6.6. The specific stack for hotspot collection is as follows: > > > > > > > > > > > > -  100.00%     0.00%  vhost-12384  [unknown]      [k] 0000000000000000 > > > > > >     - ret_from_fork > > > > > >        - 99.99% vhost_task_fn > > > > > >           - 99.98% 0xffffdc59f619876c > > > > > >              - 98.99% handle_rx_kick > > > > > >                 - 98.94% handle_rx > > > > > >                    - 94.92% tun_recvmsg > > > > > >                       - 94.76% tun_do_read > > > > > >                          - 94.62% tun_put_user_xdp_zc > > > > > >                             - 63.53% __check_object_size > > > > > >                                - 63.49% __check_object_size.part.0 > > > > > >                                     find_vmap_area > > > > > >                             - 30.02% _copy_to_iter > > > > > >                                  __arch_copy_to_user > > > > > >                    - 2.27% get_rx_bufs > > > > > >                       - 2.12% vhost_get_vq_desc > > > > > >                            1.49% __arch_copy_from_user > > > > > >                    - 0.89% peek_head_len > > > > > >                         0.54% xsk_tx_peek_desc > > > > > >                    - 0.68% vhost_add_used_and_signal_n > > > > > >                       - 0.53% eventfd_signal > > > > > >                            eventfd_signal_mask > > > > > >              - 0.94% handle_tx_kick > > > > > >                 - 0.94% handle_tx > > > > > >                    - handle_tx_copy > > > > > >                       - 0.59% vhost_tx_batch.constprop.0 > > > > > >                            0.52% tun_sendmsg > > > > > > > > > > > > It can be observed that most of the overhead is concentrated in the > > > > > > find_vmap_area function. > > > > > > > > > > > I see. Yes, it is pretty contented, since you run the v6.6 kernel. There > > > > > was a work that tends to improve it to mitigate a vmap lock contention. > > > > > See it here: https://lwn.net/Articles/956590/ > > > > > > > > > > The work was taken in the v6.9 kernel: > > > > > > > > > > > > > > > commit 38f6b9af04c4b79f81b3c2a0f76d1de94b78d7bc > > > > > Author: Uladzislau Rezki (Sony) > > > > > Date:   Tue Jan 2 19:46:23 2024 +0100 > > > > > > > > > >      mm: vmalloc: add va_alloc() helper > > > > > > > > > >      Patch series "Mitigate a vmap lock contention", v3. > > > > > > > > > >      1. Motivation > > > > > ... > > > > > > > > > > > > > > > Could you please try the v6.9 kernel on your setup? > > > > > > > > > > How to solve it, probably, it can be back-ported to the v6.6 kernel. > > > > > > > > All the vmalloc-related optimizations have already been merged into 6.6, > > > > including the set of optimization patches you suggested. Thank you very > > > > much for your input. > > > > > > > > > > It is unclear, we have backported the vmalloc optimization into our 6.6 > > > kernel before, so the above stack already with those patches and even > > > with those optimization, the find_vmap_area() is still the hotpots. > > > > > > > > Could you please check that all below patches are in your v6.6 kernel? > > Yes， > > $ git lg v6.6..HEAD --oneline mm/vmalloc.c > * 86fee542f145 mm: vmalloc: ensure vmap_block is initialised before adding > to queue > * f459a0b59f7c mm/vmalloc: fix page mapping if vm_area_alloc_pages() with > high order fallback to order 0 > * 0be7a82c2555 mm: vmalloc: fix lockdep warning > * 58b99a00d0a0 mm/vmalloc: eliminated the lock contention from twice to once > * 2c549aa32fa0 mm: vmalloc: check if a hash-index is in cpu_possible_mask > * 0bc6d608b445 mm: fix incorrect vbq reference in purge_fragmented_block > * 450f8c5270df mm/vmalloc: fix vmalloc which may return null if called with > __GFP_NOFAIL > * 2ea2bf4a18c3 mm: vmalloc: bail out early in find_vmap_area() if vmap is > not init > * bde74a3e8a71 mm/vmalloc: fix return value of vb_alloc if size is 0 > * 8c620d05b7c3 mm: vmalloc: refactor vmalloc_dump_obj() function > * b0c8281703b8 mm: vmalloc: improve description of vmap node layer > * ecc3f0bf5c5a mm: vmalloc: add a shrinker to drain vmap pools > * dd89a137f483 mm: vmalloc: set nr_nodes based on CPUs in a system > * 8e63c98d86f6 mm: vmalloc: support multiple nodes in vmallocinfo > * cc32683cef48 mm: vmalloc: support multiple nodes in vread_iter > * 54d5ce65633d mm: vmalloc: add a scan area of VA only once > * ee9c199fb859 mm: vmalloc: offload free_vmap_area_lock lock > * c2c272d78b5a mm: vmalloc: remove global purge_vmap_area_root rb-tree > * c9b39e3ffa86 mm/vmalloc: remove vmap_area_list > * 091d2493d15f mm: vmalloc: remove global vmap_area_root rb-tree > * 53f06cc34bac mm: vmalloc: move vmap_init_free_space() down in vmalloc.c > * bf24196d9ab9 mm: vmalloc: rename adjust_va_to_fit_type() function > * 6e9c94401e34 mm: vmalloc: add va_alloc() helper > * ae528eb14e9a mm: Introduce vmap_page_range() to map pages in PCI address > space > * e1dbcfaa1854 mm: Introduce VM_SPARSE kind and vm_area_[un]map_pages(). > * d3a24e7a01c4 mm: Enforce VM_IOREMAP flag and range in ioremap_page_range. > * fc9813220585 mm/vmalloc: fix the unchecked dereference warning in > vread_iter() > * a52e0157837e ascend: export interfaces required by ascend drivers > * 9b1283f2bec2 mm/vmalloc: Extend vmalloc usage about hugepage > Thank you. Then you have tons of copy_to_iter/copy_from_iter calls during your test case. Per each you need to find an area which might be really heavy. How many CPUs in a system you have? -- Uladzislau Rezki