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From: Matthew Wilcox <willy@infradead.org>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: THP backed thread stacks
Date: Fri, 17 Mar 2023 17:52:58 +0000	[thread overview]
Message-ID: <ZBSo+mLUOsKvy3rC@casper.infradead.org> (raw)
In-Reply-To: <20230306235730.GA31451@monkey>

On Mon, Mar 06, 2023 at 03:57:30PM -0800, Mike Kravetz wrote:
> One of our product teams recently experienced 'memory bloat' in their
> environment.  The application in this environment is the JVM which
> creates hundreds of threads.  Threads are ultimately created via
> pthread_create which also creates the thread stacks.  pthread attributes
> are modified so that stacks are 2MB in size.  It just so happens that
> due to allocation patterns, all their stacks are at 2MB boundaries.  The
> system has THP always set, so a huge page is allocated at the first
> (write) fault when libpthread initializes the stack.

Do you happen to have an strace (or similar) so we can understand what
the application is doing?

My understanding is that for a normal app (like, say, 'cat'), we'll
allow up to an 8MB stack, but we only create a VMA that is 4kB in size
and set the VM_GROWSDOWN flag on it (to allow it to magically grow).
Therefore we won't create a 2MB page because the VMA is too small.

It sounds like the pthread library is maybe creating a 2MB stack as
a 2MB VMA, and that's why we're seeing this behaviour?

  parent reply	other threads:[~2023-03-17 17:53 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-06 23:57 THP backed thread stacks Mike Kravetz
2023-03-07  0:15 ` Peter Xu
2023-03-07  0:40   ` Mike Kravetz
2023-03-08 19:02     ` Mike Kravetz
2023-03-09 22:38       ` Zach O'Keefe
2023-03-09 23:33         ` Mike Kravetz
2023-03-10  0:05           ` Zach O'Keefe
2023-03-10  1:40             ` William Kucharski
2023-03-10 11:25               ` David Hildenbrand
2023-03-11 12:24                 ` William Kucharski
     [not found]                 ` <20230312005549.2609-1-hdanton@sina.com>
2023-03-12  4:39                   ` William Kucharski
2023-03-10 22:02             ` Yang Shi
2023-03-07 10:10 ` David Hildenbrand
2023-03-07 19:02   ` Mike Kravetz
2023-03-07 13:36 ` Mike Rapoport
2023-03-17 17:52 ` Matthew Wilcox [this message]
2023-03-17 18:46   ` Mike Kravetz
2023-03-20 11:12     ` David Hildenbrand
2023-03-20 17:46       ` William Kucharski
2023-03-20 17:52         ` David Hildenbrand
2023-03-20 18:06         ` Mike Kravetz
2023-03-18 12:58   ` David Laight

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