linux-kernel - Re: [PATCH] hugepage: allow parallelization of the hugepage fault path

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1374193152.2076.8.camel@buesod1.americas.hpqcorp.net>
Date:	Thu, 18 Jul 2013 17:19:12 -0700
From:	Davidlohr Bueso <davidlohr.bueso@...com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Gibson <david@...son.dropbear.id.au>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Michel Lespinasse <walken@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Michal Hocko <mhocko@...e.cz>,
	"AneeshKumarK.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hillf Danton <dhillf@...il.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>,
	Eric B Munson <emunson@...bm.net>,
	Anton Blanchard <anton@...ba.org>
Subject: Re: [PATCH] hugepage: allow parallelization of the hugepage fault
 path

On Thu, 2013-07-18 at 18:07 +0900, Joonsoo Kim wrote:
> On Wed, Jul 17, 2013 at 12:50:25PM -0700, Davidlohr Bueso wrote:
> 
> > From: Davidlohr Bueso <davidlohr.bueso@...com>
> > 
> > - Cleaned up and forward ported to Linus' latest.
> > - Cache aligned mutexes.
> > - Keep non SMP systems using a single mutex.
> > 
> > It was found that this mutex can become quite contended
> > during the early phases of large databases which make use of huge pages - for instance
> > startup and initial runs. One clear example is a 1.5Gb Oracle database, where lockstat
> > reports that this mutex can be one of the top 5 most contended locks in the kernel during
> > the first few minutes:
> > 
> >     	     hugetlb_instantiation_mutex:   10678     10678
> >              ---------------------------
> >              hugetlb_instantiation_mutex    10678  [<ffffffff8115e14e>] hugetlb_fault+0x9e/0x340
> >              ---------------------------
> >              hugetlb_instantiation_mutex    10678  [<ffffffff8115e14e>] hugetlb_fault+0x9e/0x340
> > 
> > contentions:          10678
> > acquisitions:         99476
> > waittime-total: 76888911.01 us
> 
> Hello,
> I have a question :)
> 
> So, each contention takes 7.6 ms in your result.

Well, that's the total wait time. I can see your concern, but no, things
aren't *that* bad. The average amount of time spent waiting for the lock
would be 76888911.01/10678 = 7200us

> Do you map this area with VM_NORESERVE?
> If we map with VM_RESERVE, when page fault, we just dequeue a huge page from a queue and clear
> a page and then map it to a page table. So I guess, it shouldn't take so long.
> I'm wondering why it takes so long.
> 

I cannot really say. This is proprietary software. AFAICT if Oracle is
anything like Posgres, than probably no.


> And do you use 16KB-size hugepage?

No, 2Mb pages.

> If so, region handling could takes some times. If you access the area as random order,
> the number of region can be more than 90000. I guess, this can be one reason to too long
> waittime.
> 
> Thanks.

Thanks,
Davidlohr


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/