linux-kernel - Re: [[PATCH v1] 15/37] [CIFS] SMBD: Post a SMBD data transfer message with data payload

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Date:   Wed, 30 Aug 2017 01:51:38 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Long Li <longli@...rosoft.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Steve French <sfrench@...ba.org>,
        "linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>,
        "samba-technical@...ts.samba.org" <samba-technical@...ts.samba.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [[PATCH v1] 15/37] [CIFS] SMBD: Post a SMBD data transfer
 message with data payload

On Wed, Aug 30, 2017 at 02:17:56AM +0000, Long Li wrote:
> I partially addressed this issue in the V3 patch. Most of the duplicate
> code on sending path is merged.
> 
> The difficulty with translating the buffer to pages is that: I don't
> know how many pages will be translated, and how many struct page I need
> to allocate in advance to hold them. I try to avoid memory allocation
> in the I/O path as much as possible. So I keep two functions of 
> sending data: one for buffer and one for pages.

You do: you'll always need speace for  (len + PAGE_SIZE - 1) >> PAGE_SIZE
pages.

That being said: what callers even send you buffers?  In general we
should aim to work with pages for all allocations that aren't tiny.