From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [PATCH v11 07/21] dax,ext2: Replace XIP read and write with DAX I/O Date: Fri, 17 Oct 2014 15:52:14 +0000 (UTC) Message-ID: <616734389.10923.1413561134767.JavaMail.zimbra@efficios.com> References: <1411677218-29146-1-git-send-email-matthew.r.wilcox@intel.com> <1411677218-29146-8-git-send-email-matthew.r.wilcox@intel.com> <20141016095027.GE19075@thinkos.etherlink> <20141016195112.GE11522@wil.cx> <20141016223331.GA11169@wil.cx> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org To: Matthew Wilcox Return-path: In-Reply-To: <20141016223331.GA11169@wil.cx> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org ----- Original Message ----- > From: "Matthew Wilcox" > To: "Mathieu Desnoyers" > Cc: "Matthew Wilcox" , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, > linux-kernel@vger.kernel.org > Sent: Friday, October 17, 2014 12:33:31 AM > Subject: Re: [PATCH v11 07/21] dax,ext2: Replace XIP read and write with DAX I/O > > On Thu, Oct 16, 2014 at 03:51:12PM -0400, Matthew Wilcox wrote: > > On Thu, Oct 16, 2014 at 11:50:27AM +0200, Mathieu Desnoyers wrote: > > > > + if (rw == WRITE) { > > > > + if (!buffer_mapped(bh)) { > > > > + retval = -EIO; > > > > + /* FIXME: fall back to buffered I/O */ > > > > > > Fallback on buffered I/O would void guarantee about having data stored > > > into persistent memory after write returns. Not sure we actually want > > > that. > > > > Yeah, I think that comment is just stale. I can't see a way in which > > buffered I/O would succeed after DAX I/O falis. > > On further consideration, I think the whole thing is just foolish. > I don't see how get_block(create == 1) can return success *and* a buffer > that is !mapped. Perhaps a safe approach could be to put a BUG_ON() to check this assumption ? Thanks, Mathieu > > So I did this nice simplification: > > - if (rw == WRITE) { > - if (!buffer_mapped(bh)) { > - retval = -EIO; > - /* FIXME: fall back to buffered I/O > */ > - break; > - } > - hole = false; > - } else { > - hole = !buffer_written(bh); > - } > + hole = (rw != WRITE) && !buffer_written(bh); > > (compile-tested only; I'm going to run all the changes through xfstests > next week when I'm back home before sending out a v12). > -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org