From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 15 Mar 2007 13:27:23 +0100 From: Jens Axboe Subject: Re: [patch 1/2] splice: dont steal Message-ID: <20070315122723.GQ15400@kernel.dk> References: <20070314121440.GA926@wotan.suse.de> <20070315115237.GM15400@kernel.dk> <20070315122207.GA8321@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070315122207.GA8321@wotan.suse.de> Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Andrew Morton , Linux Kernel Mailing List , Linux Memory Management List List-ID: On Thu, Mar 15 2007, Nick Piggin wrote: > On Thu, Mar 15, 2007 at 12:52:37PM +0100, Jens Axboe wrote: > > On Wed, Mar 14 2007, Nick Piggin wrote: > > > Here are a couple of splice patches I found when digging in the area. > > > I could be wrong, so I'd appreciate confirmation. > > > > > > Untested other than compile, because I don't have a good splice test > > > setup. > > > > > > Considering these are data corruption / information leak issues, then > > > we could do worse than to merge them in 2.6.21 and earlier stable > > > trees. > > > > > > Does anyone really use splice stealing? > > > > That's a damn shame, I'd greatly prefer if we can try and fix it > > instead. Splice isn't really all that used yet to my knowledge, but > > stealing is one of the niftier features I think. Otherwise you're just > > copying data again. > > We should be able to allow for it with the new a_ops API I'm working > on. "Should be" and in progress stuff, is it guarenteed to get there? > Basically we can pass the page down to the filesystem, and tell it to > attempt to install that page in-place. > > The problem is that we can't just put this page here hoping the fs can > take it, becaue it might fail allocating blocks, for example. > > Anyway, we can still copy files with 1 less copy than read/write ;) It's not about 1 vs 2 copies, it's more about 0 vs 1 copy. But yes, we can file copy with less copies. > It is a nifty feature, but I think it is more of a niche than simply > saving that 1 copy, because you have to know that the source isn't > going to be used again. Well yes, same as when you free() a page. A little more tricky, but that's mainly the vm assumptions/requirements for page stealing. > But I'll try to support it with begin_write. -- Jens Axboe -- 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