From: Zheng Liu <gnehzuil.liu@gmail.com>
To: Dave Hansen <dave@sr71.net>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH] mm: madvise: MADV_POPULATE for quick pre-faulting
Date: Tue, 2 Jul 2013 10:37:48 +0800 [thread overview]
Message-ID: <20130702023748.GA10366@gmail.com> (raw)
In-Reply-To: <51D1AB6E.9030905@sr71.net>
On Mon, Jul 01, 2013 at 09:16:46AM -0700, Dave Hansen wrote:
> On 06/28/2013 07:20 PM, Zheng Liu wrote:
> >> > IOW, a process needing to do a bunch of MAP_POPULATEs isn't
> >> > parallelizable, but one using this mechanism would be.
> > I look at the code, and it seems that we will handle MAP_POPULATE flag
> > after we release mmap_sem locking in vm_mmap_pgoff():
> >
> > down_write(&mm->mmap_sem);
> > ret = do_mmap_pgoff(file, addr, len, prot, flag, pgoff,
> > &populate);
> > up_write(&mm->mmap_sem);
> > if (populate)
> > mm_populate(ret, populate);
> >
> > Am I missing something?
>
> I went and did my same test using mmap(MAP_POPULATE)/munmap() pair
> versus using MADV_POPULATE in 160 threads in parallel.
>
> MADV_POPULATE was about 10x faster in the threaded configuration.
>
> With MADV_POPULATE, the biggest cost is shipping the mmap_sem cacheline
> around so that we can write the reader count update in to it. With
> mmap(), there is a lot of _contention_ on that lock which is much, much
> more expensive than simply bouncing a cacheline around.
Thanks for your explanation.
FWIW, it would be great if we can let MAP_POPULATE flag support shared
mappings because in our product system there has a lot of applications
that uses mmap(2) and then pre-faults this mapping. Currently these
applications need to pre-fault the mapping manually.
Regards,
- Zheng
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next prev parent reply other threads:[~2013-07-02 2:19 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-27 23:16 [RFC][PATCH] mm: madvise: MADV_POPULATE for quick pre-faulting Dave Hansen
2013-06-28 5:47 ` Zheng Liu
2013-06-28 15:48 ` Dave Hansen
2013-06-29 2:20 ` Zheng Liu
2013-07-01 16:16 ` Dave Hansen
2013-07-02 2:37 ` Zheng Liu [this message]
2013-07-02 4:43 ` Dave Hansen
2013-07-02 6:06 ` Zheng Liu
2013-07-14 3:12 ` Sam Ben
2013-07-15 0:22 ` Zheng Liu
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