linux-kernel - Re: [PATCH 2/5] fdtable: Make fdarray and fdsets equal in size.

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Message-ID: <20061006064541.GA6751@in.ibm.com>
Date:	Fri, 6 Oct 2006 12:15:41 +0530
From:	Dipankar Sarma <dipankar@...ibm.com>
To:	Vadim Lobanov <vlobanov@...akeasy.net>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] fdtable: Make fdarray and fdsets equal in size.

On Thu, Oct 05, 2006 at 09:51:04PM -0700, Vadim Lobanov wrote:
> Currently, each fdtable supports three dynamically-sized arrays of data: the
> fdarray and two fdsets. The code allows the number of fds supported by the
> fdarray (fdtable->max_fds) to differ from the number of fds supported by each
> of the fdsets (fdtable->max_fdset). In practice, it is wasteful for these two
> sizes to differ: whenever we hit a limit on the smaller-capacity structure, we
> will reallocate the entire fdtable and all the dynamic arrays within it, so
> any delta in the memory used by the larger-capacity structure will never be
> touched at all. Rather than hogging this excess, we shouldn't even allocate it
> in the first place, and keep the capacities of the fdarray and the fdsets
> equal. This patch removes fdtable->max_fdset. As an added bonus, most of the
> supporting code becomes simpler.
> 
> Signed-off-by: Vadim Lobanov <vlobanov@...akeasy.net>

I agree with this patch in principle that it saves space and makes
the lockfree fdtable code simpler. However, it would be nice if
Viro or Christoph has a look at this and comment on why
we always had two different sizes.

Thanks
Dipankar
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