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Subject: Re: [PATCH v1 3/8] svcrdma: Add svc_rdma_get_context() API that is allowed to fail
From: Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <20151124065522.GC29141@infradead.org>
Date: Tue, 24 Nov 2015 09:24:51 -0500
Cc: linux-rdma@vger.kernel.org,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Message-Id: <7717B6B1-4A27-4D8A-8BCC-528CEC6DB54D@oracle.com>
References: <20151123221738.13040.26277.stgit@klimt.1015granger.net> <20151123222038.13040.61285.stgit@klimt.1015granger.net> <20151124065522.GC29141@infradead.org>
To: Christoph Hellwig <hch@infradead.org>
Sender: linux-nfs-owner@vger.kernel.org


> On Nov 24, 2015, at 1:55 AM, Christoph Hellwig <hch@infradead.org> wrote:
> 
>> +struct svc_rdma_op_ctxt *svc_rdma_get_context_gfp(struct svcxprt_rdma *xprt,
>> +						  gfp_t flags)
>> +{
>> +	struct svc_rdma_op_ctxt *ctxt;
>> +
>> +	ctxt = kmem_cache_alloc(svc_rdma_ctxt_cachep, flags);
>> +	if (!ctxt)
>> +		return NULL;
>> +	svc_rdma_init_context(xprt, ctxt);
>> +	return ctxt;
>> +}
>> +
>> +struct svc_rdma_op_ctxt *svc_rdma_get_context(struct svcxprt_rdma *xprt)
>> +{
>> +	struct svc_rdma_op_ctxt *ctxt;
>> +
>> +	ctxt = kmem_cache_alloc(svc_rdma_ctxt_cachep,
>> +				GFP_KERNEL | __GFP_NOFAIL);
>> +	svc_rdma_init_context(xprt, ctxt);
>> 	return ctxt;
> 
> Sounds like you should have just added a gfp_t argument to
> svc_rdma_get_context.

There is only one (new) call site that needs it. I can simplify
this patch as Sagi suggested before, but it seems silly to
introduce the extra clutter of adding a gfp_t argument
everywhere.


> And if we have any way to avoid the __GFP_NOFAIL
> I'd really appreciate if we could give that a try.

I’m not introducing the flag here.

Changing all the svc_rdma_get_context() call sites to handle
allocation failure (when it is already highly unlikely) is
a lot of needless work, IMO, and not related to supporting
bi-directional RPC.

--
Chuck Lever