Subject: Re: [PATCH RFC 0/5] xprtrdma Send completion batching
To: Chuck Lever <chuck.lever@oracle.com>,
        jgunthorpe@obsidianresearch.com
Cc: linux-rdma@vger.kernel.org, linux-nfs@vger.kernel.org
References: <20170905164347.11106.27140.stgit@manet.1015granger.net>
From: Sagi Grimberg <sagi@grimberg.me>
Message-ID: <1230f9d9-07c1-6d00-b197-f408712fb5c1@grimberg.me>
Date: Wed, 6 Sep 2017 14:54:20 +0300
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In-Reply-To: <20170905164347.11106.27140.stgit@manet.1015granger.net>
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Sender: linux-nfs-owner@vger.kernel.org

> Hi Jason, Sagi-

Hey Chuck,

> As we discussed a few weeks ago, this patch series implements the
> following:
> 
> - Send SGEs are now managed via lock-less, wait-free circular queues
> - Send SGEs referring to page cache pages are DMA unmapped during
>    Send completion
> - Send completions are batched to reduce interrupts, but still
>    provide a periodic heartbeat signal for SQ housekeeping
> - The circular queue prevents Send Queue overflow
> 
> The purpose of this change is to address the issue Sagi reported
> where the HCA continues to retry a delayed Send request _after_ RPC
> completion, resulting in a DMA error.

Question, what happens in direct-io for example? Can a mapped buffer be
reclaimed/free'd before the send completion arrives?