linux-kernel - Re: [PATCH] hugetlb: cond_resched for set_max_huge_pages and follow_hugetlb

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Date:	Fri, 24 Jul 2015 10:12:37 -0700
From:	Jörn Engel <joern@...estorage.com>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Spencer Baugh <sbaugh@...ern.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	David Rientjes <rientjes@...gle.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Mike Kravetz <mike.kravetz@...cle.com>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	"open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
	open list <linux-kernel@...r.kernel.org>,
	Spencer Baugh <Spencer.baugh@...estorage.com>,
	Joern Engel <joern@...fs.org>
Subject: Re: [PATCH] hugetlb: cond_resched for set_max_huge_pages and
 follow_hugetlb_page

On Fri, Jul 24, 2015 at 08:59:59AM +0200, Michal Hocko wrote:
> On Thu 23-07-15 14:54:31, Spencer Baugh wrote:
> > From: Joern Engel <joern@...fs.org>
> > 
> > ~150ms scheduler latency for both observed in the wild.
> 
> This is way to vague. Could you describe your problem somehow more,
> please?
> There are schduling points in the page allocator (when it triggers the
> reclaim), why are those not sufficient? Or do you manage to allocate
> many hugetlb pages without performing the reclaim and that leads to
> soft lockups?

We don't use transparent hugepages - they cause too much latency.
Instead we reserve somewhere around 3/4 or so of physical memory for
hugepages.  "sysctl -w vm.nr_hugepages=100000" or something similar in a
startup script.

Since it is early in boot we don't go through page reclaim.

Jörn

--
Everything should be made as simple as possible, but not simpler.
-- Albert Einstein
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