From: Zheng Liu <gnehzuil.liu@gmail.com>
To: Sam Ben <sam.bennn@gmail.com>
Cc: Dave Hansen <dave@sr71.net>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH] mm: madvise: MADV_POPULATE for quick pre-faulting
Date: Mon, 15 Jul 2013 08:22:16 +0800 [thread overview]
Message-ID: <20130715002216.GA6403@gmail.com> (raw)
In-Reply-To: <51E2173A.8080003@gmail.com>
On Sun, Jul 14, 2013 at 11:12:58AM +0800, Sam Ben wrote:
> On 07/02/2013 10:37 AM, Zheng Liu wrote:
> >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.
>
> How do you pre-fault the mapping manually in your product system? By
> walking through the file touching each page?
Yes, in our product system most applications do like this.
Regards,
- Zheng
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prev parent reply other threads:[~2013-07-15 0:03 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
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 [this message]
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