linux-kernel - Re: [LSF/MM TOPIC] Improve performance of fget/fput

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Message-ID: <20190215171619.GI12668@bombadil.infradead.org>
Date:   Fri, 15 Feb 2019 09:16:19 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Dave Watson <davejwatson@...com>
Cc:     "lsf-pc@...ts.linux-foundation.org" 
        <lsf-pc@...ts.linux-foundation.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Maged Michael <magedmichael@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [LSF/MM TOPIC] Improve performance of fget/fput

On Fri, Feb 15, 2019 at 04:38:05PM +0000, Dave Watson wrote:
> There might also be ways to rearrange the file* struct or fd table so
> that we're not taking so many cache misses for sockfd_lookup_light,
> since for sockets we don't use most of the file* struct at all.

I don't think there's too much opportunity to rearrange the fd table.
We go from task_struct->files_struct->fdtable->fd[i].  I have a plan
to use the Maple Tree data structure I'm currently working on to change
that to task_struct->files_struct->maple_node->fd[i], but it'll be
the same number of cache misses.