linux-kernel - Re: [PATCH 3/5] nfsd: Only set PF_LESS

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Message-ID: <53694E7D.6060706@redhat.com>
Date:	Tue, 06 May 2014 17:05:01 -0400
From:	Rik van Riel <riel@...hat.com>
To:	NeilBrown <neilb@...e.de>, Jan Kara <jack@...e.cz>,
	Jeff Layton <jlayton@...hat.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	Dave Chinner <david@...morbit.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Mel Gorman <mgorman@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-mm@...ck.org, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] nfsd: Only set PF_LESS_THROTTLE when really needed.

On 04/22/2014 10:40 PM, NeilBrown wrote:
> PF_LESS_THROTTLE has a very specific use case: to avoid deadlocks
> and live-locks while writing to the page cache in a loop-back
> NFS mount situation.
> 
> It therefore makes sense to *only* set PF_LESS_THROTTLE in this
> situation.
> We now know when a request came from the local-host so it could be a
> loop-back mount.  We already know when we are handling write requests,
> and when we are doing anything else.
> 
> So combine those two to allow nfsd to still be throttled (like any
> other process) in every situation except when it is known to be
> problematic.

The FUSE code has something similar, but on the "client"
side.

See BDI_CAP_STRICTLIMIT in mm/writeback.c

Would it make sense to use that flag on loopback-mounted
NFS filesystems?

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