From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from verein.lst.de ([213.95.11.211]:59292 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725927AbeLFULH (ORCPT ); Thu, 6 Dec 2018 15:11:07 -0500 Date: Thu, 6 Dec 2018 21:11:06 +0100 From: Christoph Hellwig Subject: Re: [PATCH v2] xfs: use a dedicated SLAB cache for sector sized buffer data Message-ID: <20181206201105.GB31797@lst.de> References: <20181205225147.12626-1-hch@lst.de> <20181206181139.GP24487@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181206181139.GP24487@magnolia> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: "Darrick J. Wong" Cc: Christoph Hellwig , linux-xfs@vger.kernel.org, tom.leiming@gmail.com, vkuznets@redhat.com 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.