Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 15 Feb 2019 09:16:19 -0800
From:   Matthew Wilcox <willy@infradead.org>
To:     Dave Watson <davejwatson@fb.com>
Cc:     "lsf-pc@lists.linux-foundation.org" 
        <lsf-pc@lists.linux-foundation.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Maged Michael <magedmichael@fb.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [LSF/MM TOPIC] Improve performance of fget/fput
Message-ID: <20190215171619.GI12668@bombadil.infradead.org>
References: <20190215163852.6ls6bchssazma6bm@davejwatson-mba.local>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20190215163852.6ls6bchssazma6bm@davejwatson-mba.local>
User-Agent: Mutt/1.9.2 (2017-12-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.