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Re: [PATCH v3 3/3] NFSD: Add support for encoding multiple segments

To: Anna Schumaker <anna.schumaker@xxxxxxxxxx>
Subject: Re: [PATCH v3 3/3] NFSD: Add support for encoding multiple segments
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Tue, 24 Mar 2015 10:49:16 -0700
Cc: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Marc Eshel <eshel@xxxxxxxxxx>, "linux-nfs@xxxxxxxxxxxxxxx" <linux-nfs@xxxxxxxxxxxxxxx>, linux-nfs-owner@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <CAFX2JfkybBPcqD6A8r-jOkPnkL26=NEuK3zhA6TLn-DVam+kfQ@xxxxxxxxxxxxxx>
References: <20150318205554.GA10716@xxxxxxxxxxxx> <5509E824.6070006@xxxxxxxxxx> <20150318211144.GB10716@xxxxxxxxxxxx> <OFB111A6D8.016B8BD5-ON88257E0D.001D174D-88257E0D.005268D6@xxxxxxxxxx> <20150319153627.GA20852@xxxxxxxxxxxx> <OF38D4D18B.19055EC2-ON88257E0D.0059BA03-88257E0D.005A781F@xxxxxxxxxx> <20150320151718.GD2036@xxxxxxxxxxxx> <20150320162303.GA18786@xxxxxxxxxxxxx> <20150320182621.GH2036@xxxxxxxxxxxx> <CAFX2JfkybBPcqD6A8r-jOkPnkL26=NEuK3zhA6TLn-DVam+kfQ@xxxxxxxxxxxxxx>
User-agent: Mutt/1.5.23 (2014-03-12)
On Tue, Mar 24, 2015 at 08:43:31AM -0400, Anna Schumaker wrote:
> > I don't know, and don't have profiles.  I'll either try to reproduce or
> > wait till Anna's back from vacation.
> 
> I'm using whatever functions NFSD already uses for reading files,
> which I expect go through the VFS.  Is there a flag that controls
> cache behavior?

There's the O_DIRECT flag, but that's not what I mean.  If you just
wrote to it it's a cached read, if you did unmount the filesystem after
writing, or did an echo to /proc/sys/vm/drop_caches you get uncached
read behavior.

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