From: Dave Hansen <dave.hansen@intel.com>
To: Zi Yan <ziy@nvidia.com>, Saravanan D <saravanand@fb.com>,
Xing Zhengjun <zhengjun.xing@linux.intel.com>
Cc: x86@kernel.org, dave.hansen@linux.intel.com, luto@kernel.org,
peterz@infradead.org, corbet@lwn.net, willy@infradead.org,
linux-kernel@vger.kernel.org, kernel-team@fb.com,
linux-doc@vger.kernel.org, linux-mm@kvack.org,
songliubraving@fb.com
Subject: Re: [PATCH V5] x86/mm: Tracking linear mapping split events
Date: Thu, 28 Jan 2021 08:41:26 -0800 [thread overview]
Message-ID: <15a29679-ea0b-d1c8-1a1f-698d3db35293@intel.com> (raw)
In-Reply-To: <EBB7E363-FE25-453C-89C6-9FC4A90615B9@nvidia.com>
On 1/28/21 8:33 AM, Zi Yan wrote:
>> One of the many lasting (as we don't coalesce back) sources for
>> huge page splits is tracing as the granular page
>> attribute/permission changes would force the kernel to split code
>> segments mapped to huge pages to smaller ones thereby increasing
>> the probability of TLB miss/reload even after tracing has been
>> stopped.
> It is interesting to see this statement saying splitting kernel
> direct mappings causes performance loss, when Zhengjun (cc’d) from
> Intel recently posted a kernel direct mapping performance report[1]
> saying 1GB mappings are good but not much better than 2MB and 4KB
> mappings.
No, that's not what the report said.
*Overall*, there is no clear winner between 4k, 2M and 1G. In other
words, no one page size is best for *ALL* workloads.
There were *ABSOLUTELY* individual workloads in those tests that saw
significant deltas between the direct map sizes. There are also
real-world workloads that feel the impact here.
next prev parent reply other threads:[~2021-01-28 16:46 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <BYAPR01MB40856478D5BE74CB6A7D5578CFBD9@BYAPR01MB4085.prod.exchangelabs.com>
2021-01-25 20:15 ` [PATCH] x86/mm: Tracking linear mapping split events since boot Dave Hansen
2021-01-25 20:32 ` Tejun Heo
2021-01-26 0:47 ` Dave Hansen
2021-01-26 0:53 ` Tejun Heo
2021-01-26 1:04 ` Dave Hansen
2021-01-26 1:17 ` Tejun Heo
2021-01-27 17:51 ` [PATCH V2] x86/mm: Tracking linear mapping split events Saravanan D
2021-01-27 21:03 ` Tejun Heo
2021-01-27 21:32 ` Dave Hansen
2021-01-27 21:36 ` Tejun Heo
2021-01-27 21:42 ` Saravanan D
2021-01-27 22:50 ` [PATCH V3] " Saravanan D
2021-01-27 23:00 ` Randy Dunlap
2021-01-27 23:56 ` Saravanan D
2021-01-27 23:41 ` Dave Hansen
2021-01-28 0:15 ` Saravanan D
2021-01-28 4:35 ` [PATCH V4] " Saravanan D
2021-01-28 4:51 ` Matthew Wilcox
[not found] ` <20210128104934.2916679-1-saravanand@fb.com>
2021-01-28 15:04 ` [PATCH V5] " Matthew Wilcox
2021-01-28 19:49 ` Saravanan D
2021-01-28 16:33 ` Zi Yan
2021-01-28 16:41 ` Dave Hansen [this message]
2021-01-28 16:56 ` Zi Yan
2021-01-28 16:59 ` Song Liu
[not found] ` <3aec2d10-f4c3-d07a-356f-6f1001679181@intel.com>
2021-01-28 21:20 ` Saravanan D
[not found] ` <20210128233430.1460964-1-saravanand@fb.com>
2021-01-28 23:41 ` [PATCH V6] " Tejun Heo
2021-01-29 19:27 ` Johannes Weiner
2021-02-08 23:17 ` Saravanan D
2021-02-08 23:30 ` Dave Hansen
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