linux-kernel - Re: [PATCH 1/1] mm/vmalloc: Combine all TLB flush operations of KASAN shadow virtual address into one operation

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Message-Id: <20240728141851.aece5581f6e13fb6d6280bc4@linux-foundation.org>
Date: Sun, 28 Jul 2024 14:18:51 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Adrian Huang <adrianhuang0701@...il.com>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>, Alexander Potapenko
 <glider@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov
 <dvyukov@...gle.com>, Vincenzo Frascino <vincenzo.frascino@....com>,
 Uladzislau Rezki <urezki@...il.com>, Christoph Hellwig <hch@...radead.org>,
 Baoquan He <bhe@...hat.com>, kasan-dev@...glegroups.com,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, Adrian Huang
 <ahuang12@...ovo.com>, Jiwei Sun <sunjw10@...ovo.com>
Subject: Re: [PATCH 1/1] mm/vmalloc: Combine all TLB flush operations of
 KASAN shadow virtual address into one operation

On Sat, 27 Jul 2024 00:52:46 +0800 Adrian Huang <adrianhuang0701@...il.com> wrote:

> From: Adrian Huang <ahuang12@...ovo.com>
> 
> When compiling kernel source 'make -j $(nproc)' with the up-and-running
> KASAN-enabled kernel on a 256-core machine, the following soft lockup
> is shown:
> 
> ...
>
>         # CPU  DURATION                  FUNCTION CALLS
>         # |     |   |                     |   |   |   |
>           76) $ 50412985 us |    } /* __purge_vmap_area_lazy */
>
> ...
>
>      # CPU  DURATION                  FUNCTION CALLS
>      # |     |   |                     |   |   |   |
>        23) $ 1074942 us  |    } /* __purge_vmap_area_lazy */
>        23) $ 1074950 us  |  } /* drain_vmap_area_work */
> 
>   The worst execution time of drain_vmap_area_work() is about 1 second.

Cool, thanks.

But that's still pretty dreadful and I bet there are other workloads
which will trigger the lockup detector in this path?

(And "avoiding lockup detector warnings" isn't the objective here - the
detector is merely a tool for identifying issues)