netdev - Re: [RFC PATCH 0/3] Introduce a bulk order-0 page allocator for sunrpc

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Date:   Wed, 24 Feb 2021 13:20:25 +0000
From:   Chuck Lever <chuck.lever@...cle.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
CC:     Jesper Dangaard Brouer <brouer@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-Net <netdev@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>
Subject: Re: [RFC PATCH 0/3] Introduce a bulk order-0 page allocator for
 sunrpc



> On Feb 24, 2021, at 5:26 AM, Mel Gorman <mgorman@...hsingularity.net> wrote:
> 
> This is a prototype series that introduces a bulk order-0 page allocator
> with sunrpc being the first user. The implementation is not particularly
> efficient and the intention is to iron out what the semantics of the API
> should be. That said, sunrpc was reported to have reduced allocation
> latency when refilling a pool.
> 
> As a side-note, while the implementation could be more efficient, it
> would require fairly deep surgery in numerous places. The lock scope would
> need to be significantly reduced, particularly as vmstat, per-cpu and the
> buddy allocator have different locking protocol that overal -- e.g. all
> partially depend on irqs being disabled at various points. Secondly,
> the core of the allocator deals with single pages where as both the bulk
> allocator and per-cpu allocator operate in batches. All of that has to
> be reconciled with all the existing users and their constraints (memory
> offline, CMA and cpusets being the trickiest).
> 
> In terms of semantics required by new users, my preference is that a pair
> of patches be applied -- the first which adds the required semantic to
> the bulk allocator and the second which adds the new user.
> 
> Patch 1 of this series is a cleanup to sunrpc, it could be merged
> 	separately but is included here for convenience.
> 
> Patch 2 is the prototype bulk allocator
> 
> Patch 3 is the sunrpc user. Chuck also has a patch which further caches
> 	pages but is not included in this series. It's not directly
> 	related to the bulk allocator and as it caches pages, it might
> 	have other concerns (e.g. does it need a shrinker?)
> 
> This has only been lightly tested on a low-end NFS server. It did not break
> but would benefit from an evaluation to see how much, if any, the headline
> performance changes. The biggest concern is that a light test case showed
> that there are a *lot* of bulk requests for 1 page which gets delegated to
> the normal allocator.  The same criteria should apply to any other users.
> 
> include/linux/gfp.h   |  13 +++++
> mm/page_alloc.c       | 113 +++++++++++++++++++++++++++++++++++++++++-
> net/sunrpc/svc_xprt.c |  47 ++++++++++++------
> 3 files changed, 157 insertions(+), 16 deletions(-)

Hi Mel-

Thank you for carrying the torch!


--
Chuck Lever