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: <Zqd9AsI5tWH7AukU@pc636>
Date: Mon, 29 Jul 2024 13:29:06 +0200
From: Uladzislau Rezki <urezki@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Adrian Huang <adrianhuang0701@...il.com>
Cc: Adrian Huang <adrianhuang0701@...il.com>,
	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 Sun, Jul 28, 2024 at 02:18:51PM -0700, Andrew Morton wrote:
> 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)
> 
As for 1 sec execution and worst case. I did some analysis with enabling
CONFIG_LOCK_STAT to see some waiting statistics across different locks:

See it here: https://lore.kernel.org/linux-mm/ZogS_04dP5LlRlXN@pc636/T/#m5d57f11d9f69aef5313f4efbe25415b3bae4c818

It would be really good if Adrian could run the "compiling workload" on
his big system and post the statistics here.

For example:
  a) v6.11-rc1 + KASAN.
  b) v6.11-rc1 + KASAN + patch. 

Thanks!

--
Uladzislau Rezki