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Message-ID: <Z077_8rNvTGrCb8L@pc636>
Date: Tue, 3 Dec 2024 13:39:27 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: zuoze <zuoze1@...wei.com>
Cc: Matthew Wilcox <willy@...radead.org>, gustavoars@...nel.org,
akpm@...ux-foundation.org, linux-hardening@...r.kernel.org,
linux-mm@...ck.org, keescook@...omium.org, urezki@...il.com,
wangkefeng.wang@...wei.com
Subject: Re: [PATCH -next] mm: usercopy: add a debugfs interface to bypass
the vmalloc check.
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:
<snip>
commit 38f6b9af04c4b79f81b3c2a0f76d1de94b78d7bc
Author: Uladzislau Rezki (Sony) <urezki@...il.com>
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
...
<snip>
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.
Thanks!
--
Uladzislau Rezki
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