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From: Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
To: David Dillow <dillowda-1Heg1YXhbW8@public.gmane.org>
Cc: Or Gerlitz <ogerlitz-smomgflXvOZWk0Htik3J/w@public.gmane.org>,
	linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Roland Dreier <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org>,
	Eli Cohen <eli-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>
Subject: Re: IB: increase DMA max_segment_size on Mellanox hardware
Date: Tue, 18 Jan 2011 11:01:29 -0700	[thread overview]
Message-ID: <20110118180129.GH995@obsidianresearch.com> (raw)
In-Reply-To: <1295353524.3051.121.camel-1q1vX8mYZiGLUyTwlgNVppKKF0rrzTr+@public.gmane.org>

On Tue, Jan 18, 2011 at 07:25:24AM -0500, David Dillow wrote:

> > Also when working with direct I/O from user space and/or under file-system,
> > did you really see many BIOs that can be merged? I was under the impression,
> > that (specifically after some time the system is active) for the most case, 
> > I get totally scattered SGs, whose pages can't be coalesced at all.
> 
> I would expect that to be a common case, but there are systems out there
> that this is not an issue. They typically allocate buffers early on when
> they can be contiguous, and just keep reusing those.

It has become really easy to use hugetlb now, you can just mmap
anonymous memory with MAP_HUGETLB and you get 2M pages. If an app is
using O_DIRECT it seem worth making an attempt to use huge pages..

IIRC databases are already doing this.

Jason
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  parent reply	other threads:[~2011-01-18 18:01 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-17  2:09 IB: increase DMA max_segment_size on Mellanox hardware David Dillow
     [not found] ` <1295230184.2574.26.camel-1q1vX8mYZiGLUyTwlgNVppKKF0rrzTr+@public.gmane.org>
2011-01-17 11:16   ` Or Gerlitz
     [not found]     ` <4D342510.80701-smomgflXvOZWk0Htik3J/w@public.gmane.org>
2011-01-18  2:46       ` David Dillow
     [not found]         ` <1295318783.3051.81.camel-1q1vX8mYZiGLUyTwlgNVppKKF0rrzTr+@public.gmane.org>
2011-01-18  5:22           ` Jason Gunthorpe
2011-01-18  7:16           ` Or Gerlitz
     [not found]             ` <4D353E5E.2020500-smomgflXvOZWk0Htik3J/w@public.gmane.org>
2011-01-18 12:25               ` David Dillow
     [not found]                 ` <1295353524.3051.121.camel-1q1vX8mYZiGLUyTwlgNVppKKF0rrzTr+@public.gmane.org>
2011-01-18 18:01                   ` Jason Gunthorpe [this message]
2011-01-20 10:14                   ` Or Gerlitz
     [not found]                     ` <4D380AF2.4010905-smomgflXvOZWk0Htik3J/w@public.gmane.org>
2011-01-20 12:15                       ` David Dillow
     [not found]                         ` <1295525737.22825.24.camel-1q1vX8mYZiGLUyTwlgNVppKKF0rrzTr+@public.gmane.org>
2011-01-24 15:18                           ` Or Gerlitz
     [not found]                             ` <4D3D9845.4050803-smomgflXvOZWk0Htik3J/w@public.gmane.org>
2011-01-24 19:36                               ` David Dillow
     [not found]                                 ` <1295897819.29946.17.camel-FqX9LgGZnHWDB2HL1qBt2PIbXMQ5te18@public.gmane.org>
2011-02-17  1:06                                   ` David Dillow
     [not found]                                     ` <1297904810.8833.44.camel-FqX9LgGZnHWDB2HL1qBt2PIbXMQ5te18@public.gmane.org>
2011-03-16 19:17                                       ` Or Gerlitz
2011-01-20 10:18           ` Or Gerlitz
     [not found]             ` <4D380BDC.5080002-smomgflXvOZWk0Htik3J/w@public.gmane.org>
2011-01-20 12:25               ` David Dillow
2011-03-22  8:01   ` Or Gerlitz
     [not found]     ` <4D885748.6060600-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
2011-03-22 12:51       ` David Dillow

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