From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752901AbaE1LXb (ORCPT ); Wed, 28 May 2014 07:23:31 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:33361 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752292AbaE1LXa (ORCPT ); Wed, 28 May 2014 07:23:30 -0400 Date: Wed, 28 May 2014 04:23:29 -0700 From: Christoph Hellwig To: Vaughan Cao Cc: James.Bottomley@HansenPartnership.com, linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] notify block layer when using temporary change to cache_type Message-ID: <20140528112329.GA11953@infradead.org> References: <1401190754-6822-1-git-send-email-vaughan.cao@oracle.com> <1401207496.14454.90.camel@dabdike> <1401253107-16138-1-git-send-email-vaughan.cao@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1401253107-16138-1-git-send-email-vaughan.cao@oracle.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 28, 2014 at 12:58:27PM +0800, Vaughan Cao wrote: > No, I just want to keep the modification as small as possible. Checked > the actions of sd_revalidate_disk() again, it seems no harm to call it > from here. Also actual actions are skipped in sd_read_cache_type() if > cache_override!=0, so I suppose your original plan is to jump to > sd_revalidate_disk() from here. I think the right fix is to factor out a helper like: static void sd_set_flush_flag(struct scsi_disk *sdkp) { unsigned flush = 0; if (sdkp->WCE) { flush |= REQ_FLUSH; if (sdkp->DPOFUA) flush |= REQ_FUA; } blk_queue_flush(sdkp->disk->queue, flush); } which can be called from sd_revalidate_disk and cache_type_store. > > However, that way may not be acceptable after further code review. > Changing the sdkp->WCE,RCD will cause these real parameters of the > underlying device *lost*. In sd_shutdown() and sd_suspend_common(), we > need them to call sd_sync_cache() if necessary. I don't think this > action is avoidable, just for the performance issue to solve. And we > can't change the mode just by setting q->flush_flags while leave > sdkp->WCE,RCD untouched either, because cache_type_show() needs > sdkp->WCE,RCD to present the temporary config to userspace. If the user overrides the cache type he should expect data not to be flushed, so I don't really think this is na issue. Even if it is it should be a separate issue as it already exists before your patch.