linux-kernel - Re: [PATCH -next] mm/hugetlb_cgroup: introduce peak and rsvd.peak to v2

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Message-ID: <6843023e-3e80-0c1c-6aab-b386ffebd668@huawei.com>
Date: Wed, 3 Jul 2024 10:45:56 +0800
From: xiujianfeng <xiujianfeng@...wei.com>
To: Andrew Morton <akpm@...ux-foundation.org>
CC: <tj@...nel.org>, <lizefan.x@...edance.com>, <hannes@...xchg.org>,
	<corbet@....net>, <cgroups@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH -next] mm/hugetlb_cgroup: introduce peak and rsvd.peak to
 v2

On 2024/7/3 9:58, Andrew Morton wrote:
> On Tue, 2 Jul 2024 12:57:28 +0000 Xiu Jianfeng <xiujianfeng@...wei.com> wrote:
> 
>> Introduce peak and rsvd.peak to v2 to show the historical maximum
>> usage of resources, as in some scenarios it is necessary to configure
>> the value of max/rsvd.max based on the peak usage of resources.
> 
> "in some scenarios it is necessary" is not a strong statement.  It
> would be helpful to fully describe these scenarios so that others can
> better understand the value of this change.
> 

Hi Andrew,

Is the following description acceptable for you?

Since HugeTLB doesn't support page reclaim, enforcing the limit at
page fault time implies that, the application will get SIGBUS signal
if it tries to fault in HugeTLB pages beyond its limit. Therefore the
application needs to know exactly how many HugeTLB pages it uses before
hand, and the sysadmin needs to make sure that there are enough
available on the machine for all the users to avoid processes getting
SIGBUS.

When running some open-source software, it may not be possible to know
the exact amount of hugetlb it consumes, so cannot correctly configure
the max value. If there is a peak metric, we can run the open-source
software first and then configure the max based on the peak value.
In cgroup v1, the hugetlb controller provides the max_usage_in_bytes
and rsvd.max_usage_in_bytes interface to display the historical maximum
usage, so introduce peak and rsvd.peak to v2 to address this issue.