From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2120.oracle.com ([156.151.31.85]:58728 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726129AbeLFU0X (ORCPT ); Thu, 6 Dec 2018 15:26:23 -0500 Date: Thu, 6 Dec 2018 12:26:14 -0800 From: "Darrick J. Wong" Subject: Re: [PATCH v2] xfs: use a dedicated SLAB cache for sector sized buffer data Message-ID: <20181206202614.GQ24487@magnolia> References: <20181205225147.12626-1-hch@lst.de> <20181206181139.GP24487@magnolia> <20181206201105.GB31797@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181206201105.GB31797@lst.de> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Christoph Hellwig Cc: linux-xfs@vger.kernel.org, tom.leiming@gmail.com, vkuznets@redhat.com On Thu, Dec 06, 2018 at 09:11:06PM +0100, Christoph Hellwig wrote: > On Thu, Dec 06, 2018 at 10:11:39AM -0800, Darrick J. Wong wrote: > > I think this has the same problem that Dave complained about back in > > October -- if I have a hard disk with 512b sectors, a xfs with 4k > > blocks, and mount it on a machine with 64k pages, then single-sector > > buffers will get a small slab allocation, but single-fsb buffers will > > now fall back to grabbing a 64k page to hold 4k worth of data. > > > > Even if we add a second slab for single-fsb blocks, we'll run into the > > same problem if the filesystem contains multi-block directory blocks, so > > then we'd potentially need a third slab, and... is there a way to ask a > > slab allocator for multiple contiguous objects totalling less than > > PAGE_SIZE bytes? > > No, unfortunately there is not. And the sad part is that generally it > will give you aligned ones, just with slub debugging turned on it won't. Hmmm. I guess we could declare three slabs then -- sector size, fsb size, and dir fsb size? This is getting kinda spidery now though. Is three too weird? --D